diff --git a/README.md b/README.md
index 4aa074087..1d095b02e 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ and/or:
 
     Install-Package System.IO.Abstractions.TestingHelpers
 
-At the core of the library is IFileSystem and FileSystem. Instead of calling methods like `File.ReadAllText` directly, use `IFileSystem.File.ReadAllText`. We have exactly the same API, except that ours is injectable and testable.
+At the core of the library is `IFileSystem` and `FileSystem`. Instead of calling methods like `File.ReadAllText` directly, use `IFileSystem.File.ReadAllText`. We have exactly the same API, except that ours is injectable and testable.
 
 ```csharp
 public class MyComponent
@@ -28,7 +28,7 @@ public class MyComponent
     /// <summary>Create MyComponent</summary>
     public MyComponent() : this( 
         fileSystem: new FileSystem() //use default implementation which calls System.IO
-    ) 
+    )
     {
     }
 
@@ -74,17 +74,67 @@ public void MyComponent_Validate_ShouldThrowNotSupportedExceptionIfTestingIsNotA
     Assert.Fail("The expected exception was not thrown.");
 }
 ```
+
 We even support casting from the .NET Framework's untestable types to our testable wrappers:
 
 ```csharp
-FileInfo SomeBadApiMethodThatReturnsFileInfo()
+FileInfo SomeApiMethodThatReturnsFileInfo()
 {
     return new FileInfo("a");
 }
 
 void MyFancyMethod()
 {
-    var testableFileInfo = (FileInfoBase)SomeBadApiMethodThatReturnsFileInfo();
+    var testableFileInfo = (FileInfoBase)SomeApiMethodThatReturnsFileInfo();
     ...
 }
 ```
+
+Since version 4.0 the top-level APIs expose interfaces instead of abstract base classes (these still exist, though), allowing you to completely mock the file system. Here's a small example, using [Moq](https://github.com/moq/moq4):
+
+```csharp
+[Test]
+public void Test1()
+{
+    var watcher = Mock.Of<IFileSystemWatcher>();
+    var file = Mock.Of<IFile>();
+
+    Mock.Get(file).Setup(f => f.Exists(It.IsAny<string>())).Returns(true);
+    Mock.Get(file).Setup(f => f.ReadAllText(It.IsAny<string>())).Throws<OutOfMemoryException>();
+
+    var unitUnderTest = new SomeClassUsingFileSystemWatcher(watcher, file);
+
+    Assert.Throws<OutOfMemoryException>(() => {
+        Mock.Get(watcher).Raise(w => w.Created += null, new System.IO.FileSystemEventArgs(System.IO.WatcherChangeTypes.Created, @"C:\Some\Directory", "Some.File"));
+    });
+
+    Mock.Get(file).Verify(f => f.Exists(It.IsAny<string>()), Times.Once);
+
+    Assert.True(unitUnderTest.FileWasCreated);
+}
+
+public class SomeClassUsingFileSystemWatcher
+{
+    private readonly IFileSystemWatcher _watcher;
+    private readonly IFile _file;
+
+    public bool FileWasCreated { get; private set; }
+
+    public SomeClassUsingFileSystemWatcher(IFileSystemWatcher watcher, IFile file)
+    {
+        this._file = file;
+        this._watcher = watcher;
+        this._watcher.Created += Watcher_Created;
+    }
+
+    private void Watcher_Created(object sender, System.IO.FileSystemEventArgs e)
+    {
+        FileWasCreated = true;
+
+        if(_file.Exists(e.FullPath))
+        {
+            var text = _file.ReadAllText(e.FullPath);
+        }
+    }
+}
+```
\ No newline at end of file
diff --git a/System.IO.Abstractions.TestingHelpers.Tests/MockDirectoryArgumentPathTests.cs b/System.IO.Abstractions.TestingHelpers.Tests/MockDirectoryArgumentPathTests.cs
index b390fbf70..a9401f093 100644
--- a/System.IO.Abstractions.TestingHelpers.Tests/MockDirectoryArgumentPathTests.cs
+++ b/System.IO.Abstractions.TestingHelpers.Tests/MockDirectoryArgumentPathTests.cs
@@ -6,7 +6,7 @@ namespace System.IO.Abstractions.TestingHelpers.Tests
 {
     public class MockDirectoryArgumentPathTests
     {
-        private static IEnumerable<Action<DirectoryBase>> GetFileSystemActionsForArgumentNullException()
+        private static IEnumerable<Action<IDirectory>> GetFileSystemActionsForArgumentNullException()
         {
             yield return ds => ds.Delete(null);
             yield return ds => ds.Delete(null, true);
@@ -26,7 +26,7 @@ private static IEnumerable<Action<DirectoryBase>> GetFileSystemActionsForArgumen
         }
 
         [TestCaseSource("GetFileSystemActionsForArgumentNullException")]
-        public void Operations_ShouldThrowArgumentNullExceptionIfPathIsNull(Action<DirectoryBase> action)
+        public void Operations_ShouldThrowArgumentNullExceptionIfPathIsNull(Action<IDirectory> action)
         {
             // Arrange
             var fileSystem = new MockFileSystem();
diff --git a/System.IO.Abstractions.TestingHelpers.Tests/MockFileArgumentPathTests.cs b/System.IO.Abstractions.TestingHelpers.Tests/MockFileArgumentPathTests.cs
index 0d97899f7..8e368689b 100644
--- a/System.IO.Abstractions.TestingHelpers.Tests/MockFileArgumentPathTests.cs
+++ b/System.IO.Abstractions.TestingHelpers.Tests/MockFileArgumentPathTests.cs
@@ -7,7 +7,7 @@ namespace System.IO.Abstractions.TestingHelpers.Tests
 {
     public class MockFileArgumentPathTests
     {
-        private static IEnumerable<Action<FileBase>> GetFileSystemActionsForArgumentNullException()
+        private static IEnumerable<Action<IFile>> GetFileSystemActionsForArgumentNullException()
         {
             yield return fs => fs.AppendAllLines(null, new[] { "does not matter" });
             yield return fs => fs.AppendAllLines(null, new[] { "does not matter" }, Encoding.ASCII);
@@ -57,7 +57,7 @@ private static IEnumerable<Action<FileBase>> GetFileSystemActionsForArgumentNull
         }
 
         [TestCaseSource("GetFileSystemActionsForArgumentNullException")]
-        public void Operations_ShouldThrowArgumentNullExceptionIfPathIsNull(Action<FileBase> action)
+        public void Operations_ShouldThrowArgumentNullExceptionIfPathIsNull(Action<IFile> action)
         {
             // Arrange
             var fileSystem = new MockFileSystem();
diff --git a/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs b/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs
index 108ef2fe7..d5fd008be 100644
--- a/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs
+++ b/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs
@@ -352,8 +352,8 @@ public void MockFileSystem_FileSystemWatcher_ShouldBeAssignable()
 
         private class TestFileSystemWatcherFactory : IFileSystemWatcherFactory
         {
-            public FileSystemWatcherBase CreateNew() => new TestFileSystemWatcher(null);
-            public FileSystemWatcherBase FromPath(string path) => new TestFileSystemWatcher(path);
+            public IFileSystemWatcher CreateNew() => new TestFileSystemWatcher(null);
+            public IFileSystemWatcher FromPath(string path) => new TestFileSystemWatcher(path);
         }
 
         private class TestFileSystemWatcher : FileSystemWatcherBase
diff --git a/System.IO.Abstractions.TestingHelpers/IMockFileDataAccessor.cs b/System.IO.Abstractions.TestingHelpers/IMockFileDataAccessor.cs
index 6c2c6350a..d42063fd8 100644
--- a/System.IO.Abstractions.TestingHelpers/IMockFileDataAccessor.cs
+++ b/System.IO.Abstractions.TestingHelpers/IMockFileDataAccessor.cs
@@ -56,10 +56,10 @@ public interface IMockFileDataAccessor
 
         StringOperations StringOperations { get; }
 
-        FileBase File { get; }
-        DirectoryBase Directory { get; }
+        IFile File { get; }
+        IDirectory Directory { get; }
         IFileInfoFactory FileInfo {get; }
-        PathBase Path { get; }
+        IPath Path { get; }
         IDirectoryInfoFactory DirectoryInfo { get; }
         IDriveInfoFactory DriveInfo { get; }
 
diff --git a/System.IO.Abstractions.TestingHelpers/MockDirectory.cs b/System.IO.Abstractions.TestingHelpers/MockDirectory.cs
index cd3b2519b..cffef30ab 100644
--- a/System.IO.Abstractions.TestingHelpers/MockDirectory.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockDirectory.cs
@@ -25,19 +25,19 @@ public MockDirectory(IMockFileDataAccessor mockFileDataAccessor, string currentD
             this.mockFileDataAccessor = mockFileDataAccessor ?? throw new ArgumentNullException(nameof(mockFileDataAccessor));
         }
 
-        public override DirectoryInfoBase CreateDirectory(string path)
+        public override IDirectoryInfo CreateDirectory(string path)
         {
             return CreateDirectoryInternal(path, null);
         }
 
 #if NET40
-        public override DirectoryInfoBase CreateDirectory(string path, DirectorySecurity directorySecurity)
+        public override IDirectoryInfo CreateDirectory(string path, DirectorySecurity directorySecurity)
         {
             return CreateDirectoryInternal(path, directorySecurity);
         }
 #endif
 
-        private DirectoryInfoBase CreateDirectoryInternal(string path, DirectorySecurity directorySecurity)
+        private IDirectoryInfo CreateDirectoryInternal(string path, DirectorySecurity directorySecurity)
         {
             if (path == null)
             {
@@ -312,7 +312,7 @@ public override string[] GetLogicalDrives()
         }
 #endif
 
-        public override DirectoryInfoBase GetParent(string path)
+        public override IDirectoryInfo GetParent(string path)
         {
             if (path == null)
             {
diff --git a/System.IO.Abstractions.TestingHelpers/MockDirectoryInfo.cs b/System.IO.Abstractions.TestingHelpers/MockDirectoryInfo.cs
index a105d2217..ac6c94ad4 100644
--- a/System.IO.Abstractions.TestingHelpers/MockDirectoryInfo.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockDirectoryInfo.cs
@@ -127,13 +127,13 @@ public override void Create(DirectorySecurity directorySecurity)
         }
 #endif
 
-        public override DirectoryInfoBase CreateSubdirectory(string path)
+        public override IDirectoryInfo CreateSubdirectory(string path)
         {
             return mockFileDataAccessor.Directory.CreateDirectory(Path.Combine(FullName, path));
         }
 
 #if NET40
-        public override DirectoryInfoBase CreateSubdirectory(string path, DirectorySecurity directorySecurity)
+        public override IDirectoryInfo CreateSubdirectory(string path, DirectorySecurity directorySecurity)
         {
             return mockFileDataAccessor.Directory.CreateDirectory(Path.Combine(FullName, path), directorySecurity);
         }
@@ -144,47 +144,47 @@ public override void Delete(bool recursive)
             mockFileDataAccessor.Directory.Delete(directoryPath, recursive);
         }
 
-        public override IEnumerable<DirectoryInfoBase> EnumerateDirectories()
+        public override IEnumerable<IDirectoryInfo> EnumerateDirectories()
         {
             return GetDirectories();
         }
 
-        public override IEnumerable<DirectoryInfoBase> EnumerateDirectories(string searchPattern)
+        public override IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern)
         {
             return GetDirectories(searchPattern);
         }
 
-        public override IEnumerable<DirectoryInfoBase> EnumerateDirectories(string searchPattern, SearchOption searchOption)
+        public override IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern, SearchOption searchOption)
         {
             return GetDirectories(searchPattern, searchOption);
         }
 
-        public override IEnumerable<FileInfoBase> EnumerateFiles()
+        public override IEnumerable<IFileInfo> EnumerateFiles()
         {
             return GetFiles();
         }
 
-        public override IEnumerable<FileInfoBase> EnumerateFiles(string searchPattern)
+        public override IEnumerable<IFileInfo> EnumerateFiles(string searchPattern)
         {
             return GetFiles(searchPattern);
         }
 
-        public override IEnumerable<FileInfoBase> EnumerateFiles(string searchPattern, SearchOption searchOption)
+        public override IEnumerable<IFileInfo> EnumerateFiles(string searchPattern, SearchOption searchOption)
         {
             return GetFiles(searchPattern, searchOption);
         }
 
-        public override IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos()
+        public override IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos()
         {
             return GetFileSystemInfos();
         }
 
-        public override IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos(string searchPattern)
+        public override IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern)
         {
             return GetFileSystemInfos(searchPattern);
         }
 
-        public override IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos(string searchPattern, SearchOption searchOption)
+        public override IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern, SearchOption searchOption)
         {
             return GetFileSystemInfos(searchPattern, searchOption);
         }
@@ -199,17 +199,17 @@ public override DirectorySecurity GetAccessControl(AccessControlSections include
             return mockFileDataAccessor.Directory.GetAccessControl(directoryPath, includeSections);
         }
 
-        public override DirectoryInfoBase[] GetDirectories()
+        public override IDirectoryInfo[] GetDirectories()
         {
             return ConvertStringsToDirectories(mockFileDataAccessor.Directory.GetDirectories(directoryPath));
         }
 
-        public override DirectoryInfoBase[] GetDirectories(string searchPattern)
+        public override IDirectoryInfo[] GetDirectories(string searchPattern)
         {
             return ConvertStringsToDirectories(mockFileDataAccessor.Directory.GetDirectories(directoryPath, searchPattern));
         }
 
-        public override DirectoryInfoBase[] GetDirectories(string searchPattern, SearchOption searchOption)
+        public override IDirectoryInfo[] GetDirectories(string searchPattern, SearchOption searchOption)
         {
             return ConvertStringsToDirectories(mockFileDataAccessor.Directory.GetDirectories(directoryPath, searchPattern, searchOption));
         }
@@ -222,41 +222,41 @@ private DirectoryInfoBase[] ConvertStringsToDirectories(IEnumerable<string> path
                 .ToArray();
         }
 
-        public override FileInfoBase[] GetFiles()
+        public override IFileInfo[] GetFiles()
         {
             return ConvertStringsToFiles(mockFileDataAccessor.Directory.GetFiles(FullName));
         }
 
-        public override FileInfoBase[] GetFiles(string searchPattern)
+        public override IFileInfo[] GetFiles(string searchPattern)
         {
             return ConvertStringsToFiles(mockFileDataAccessor.Directory.GetFiles(FullName, searchPattern));
         }
 
-        public override FileInfoBase[] GetFiles(string searchPattern, SearchOption searchOption)
+        public override IFileInfo[] GetFiles(string searchPattern, SearchOption searchOption)
         {
             return ConvertStringsToFiles(mockFileDataAccessor.Directory.GetFiles(FullName, searchPattern, searchOption));
         }
 
-        FileInfoBase[] ConvertStringsToFiles(IEnumerable<string> paths)
+        IFileInfo[] ConvertStringsToFiles(IEnumerable<string> paths)
         {
             return paths
                   .Select(mockFileDataAccessor.FileInfo.FromFileName)
                   .ToArray();
         }
 
-        public override FileSystemInfoBase[] GetFileSystemInfos()
+        public override IFileSystemInfo[] GetFileSystemInfos()
         {
             return GetFileSystemInfos("*");
         }
 
-        public override FileSystemInfoBase[] GetFileSystemInfos(string searchPattern)
+        public override IFileSystemInfo[] GetFileSystemInfos(string searchPattern)
         {
             return GetFileSystemInfos(searchPattern, SearchOption.TopDirectoryOnly);
         }
 
-        public override FileSystemInfoBase[] GetFileSystemInfos(string searchPattern, SearchOption searchOption)
+        public override IFileSystemInfo[] GetFileSystemInfos(string searchPattern, SearchOption searchOption)
         {
-            return GetDirectories(searchPattern, searchOption).OfType<FileSystemInfoBase>().Concat(GetFiles(searchPattern, searchOption)).ToArray();
+            return GetDirectories(searchPattern, searchOption).OfType<IFileSystemInfo>().Concat(GetFiles(searchPattern, searchOption)).ToArray();
         }
 
         public override void MoveTo(string destDirName)
@@ -269,7 +269,7 @@ public override void SetAccessControl(DirectorySecurity directorySecurity)
             mockFileDataAccessor.Directory.SetAccessControl(directoryPath, directorySecurity);
         }
 
-        public override DirectoryInfoBase Parent
+        public override IDirectoryInfo Parent
         {
             get
             {
@@ -277,7 +277,7 @@ public override DirectoryInfoBase Parent
             }
         }
 
-        public override DirectoryInfoBase Root
+        public override IDirectoryInfo Root
         {
             get
             {
diff --git a/System.IO.Abstractions.TestingHelpers/MockDirectoryInfoFactory.cs b/System.IO.Abstractions.TestingHelpers/MockDirectoryInfoFactory.cs
index 51f638feb..b42080e37 100644
--- a/System.IO.Abstractions.TestingHelpers/MockDirectoryInfoFactory.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockDirectoryInfoFactory.cs
@@ -10,7 +10,7 @@ public MockDirectoryInfoFactory(IMockFileDataAccessor mockFileSystem)
             this.mockFileSystem = mockFileSystem;
         }
 
-        public DirectoryInfoBase FromDirectoryName(string directoryName)
+        public IDirectoryInfo FromDirectoryName(string directoryName)
         {
             return new MockDirectoryInfo(mockFileSystem, directoryName);
         }
diff --git a/System.IO.Abstractions.TestingHelpers/MockDriveInfo.cs b/System.IO.Abstractions.TestingHelpers/MockDriveInfo.cs
index 61ec413b4..6b9d8a870 100644
--- a/System.IO.Abstractions.TestingHelpers/MockDriveInfo.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockDriveInfo.cs
@@ -44,7 +44,7 @@ public MockDriveInfo(IMockFileDataAccessor mockFileDataAccessor, string name) :
         public new bool IsReady { get; protected set; }
         public override string Name { get; protected set; }
 
-        public override DirectoryInfoBase RootDirectory
+        public override IDirectoryInfo RootDirectory
         {
             get
             {
diff --git a/System.IO.Abstractions.TestingHelpers/MockDriveInfoFactory.cs b/System.IO.Abstractions.TestingHelpers/MockDriveInfoFactory.cs
index bd1596a00..adc8cb0d5 100644
--- a/System.IO.Abstractions.TestingHelpers/MockDriveInfoFactory.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockDriveInfoFactory.cs
@@ -12,7 +12,7 @@ public MockDriveInfoFactory(IMockFileDataAccessor mockFileSystem)
             this.mockFileSystem = mockFileSystem ?? throw new ArgumentNullException(nameof(mockFileSystem));
         }
 
-        public DriveInfoBase[] GetDrives()
+        public IDriveInfo[] GetDrives()
         {
             var driveLetters = new HashSet<string>(new DriveEqualityComparer(mockFileSystem));
             foreach (var path in mockFileSystem.AllPaths)
@@ -38,7 +38,7 @@ public DriveInfoBase[] GetDrives()
             return result.ToArray();
         }
 
-        public DriveInfoBase FromDriveName(string driveName)
+        public IDriveInfo FromDriveName(string driveName)
         {
             var drive = mockFileSystem.Path.GetPathRoot(driveName);
 
diff --git a/System.IO.Abstractions.TestingHelpers/MockFileInfo.cs b/System.IO.Abstractions.TestingHelpers/MockFileInfo.cs
index 34691af01..6d5da990e 100644
--- a/System.IO.Abstractions.TestingHelpers/MockFileInfo.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockFileInfo.cs
@@ -153,12 +153,12 @@ public override StreamWriter AppendText()
             return new StreamWriter(new MockFileStream(mockFileSystem, FullName, MockFileStream.StreamType.APPEND));
         }
 
-        public override FileInfoBase CopyTo(string destFileName)
+        public override IFileInfo CopyTo(string destFileName)
         {
             return CopyTo(destFileName, false);
         }
 
-        public override FileInfoBase CopyTo(string destFileName, bool overwrite)
+        public override IFileInfo CopyTo(string destFileName, bool overwrite)
         {
             if (!Exists)
             {
@@ -251,12 +251,12 @@ public override Stream OpenWrite()
         }
 
 #if NET40
-        public override FileInfoBase Replace(string destinationFileName, string destinationBackupFileName)
+        public override IFileInfo Replace(string destinationFileName, string destinationBackupFileName)
         {
             return Replace(destinationFileName, destinationBackupFileName, false);
         }
 
-        public override FileInfoBase Replace(string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors)
+        public override IFileInfo Replace(string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors)
         {
             mockFileSystem.File.Replace(path, destinationFileName, destinationBackupFileName, ignoreMetadataErrors);
             return mockFileSystem.FileInfo.FromFileName(destinationFileName);
@@ -268,7 +268,7 @@ public override void SetAccessControl(FileSecurity fileSecurity)
             mockFileSystem.File.SetAccessControl(this.path, fileSecurity);
         }
 
-        public override DirectoryInfoBase Directory
+        public override IDirectoryInfo Directory
         {
             get
             {
diff --git a/System.IO.Abstractions.TestingHelpers/MockFileInfoFactory.cs b/System.IO.Abstractions.TestingHelpers/MockFileInfoFactory.cs
index ffdec272f..9c5504ccd 100644
--- a/System.IO.Abstractions.TestingHelpers/MockFileInfoFactory.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockFileInfoFactory.cs
@@ -10,7 +10,7 @@ public MockFileInfoFactory(IMockFileDataAccessor mockFileSystem)
             this.mockFileSystem = mockFileSystem ?? throw new ArgumentNullException(nameof(mockFileSystem));
         }
 
-        public FileInfoBase FromFileName(string fileName)
+        public IFileInfo FromFileName(string fileName)
         {
             return new MockFileInfo(mockFileSystem, fileName);
         }
diff --git a/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs b/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs
index 8e4edc7d1..83957f0d8 100644
--- a/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs
@@ -53,11 +53,11 @@ public MockFileSystem(IDictionary<string, MockFileData> files, string currentDir
         }
 
         public StringOperations StringOperations { get; }
-        public FileBase File { get; }
-        public DirectoryBase Directory { get; }
+        public IFile File { get; }
+        public IDirectory Directory { get; }
         public IFileInfoFactory FileInfo { get; }
         public IFileStreamFactory FileStream { get; }
-        public PathBase Path { get; }
+        public IPath Path { get; }
         public IDirectoryInfoFactory DirectoryInfo { get; }
         public IDriveInfoFactory DriveInfo { get; }
         public IFileSystemWatcherFactory FileSystemWatcher { get; set; }
diff --git a/System.IO.Abstractions.TestingHelpers/MockFileSystemWatcherFactory.cs b/System.IO.Abstractions.TestingHelpers/MockFileSystemWatcherFactory.cs
index fa832ba13..247114442 100644
--- a/System.IO.Abstractions.TestingHelpers/MockFileSystemWatcherFactory.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockFileSystemWatcherFactory.cs
@@ -3,10 +3,10 @@
     [Serializable]
     public class MockFileSystemWatcherFactory : IFileSystemWatcherFactory
     {
-        public FileSystemWatcherBase CreateNew() =>
+        public IFileSystemWatcher CreateNew() =>
             throw new NotImplementedException(StringResources.Manager.GetString("FILE_SYSTEM_WATCHER_NOT_IMPLEMENTED_EXCEPTION"));
 
-        public FileSystemWatcherBase FromPath(string path) =>
+        public IFileSystemWatcher FromPath(string path) =>
             throw new NotImplementedException(StringResources.Manager.GetString("FILE_SYSTEM_WATCHER_NOT_IMPLEMENTED_EXCEPTION"));
     }
 }
diff --git a/System.IO.Abstractions/DirectoryBase.cs b/System.IO.Abstractions/DirectoryBase.cs
index c4a9b08fc..8c8283cdc 100644
--- a/System.IO.Abstractions/DirectoryBase.cs
+++ b/System.IO.Abstractions/DirectoryBase.cs
@@ -5,7 +5,7 @@ namespace System.IO.Abstractions
 {
     /// <inheritdoc cref="Directory"/>
     [Serializable]
-    public abstract class DirectoryBase
+    public abstract class DirectoryBase : IDirectory
     {
         protected DirectoryBase(IFileSystem fileSystem)
         {
@@ -21,11 +21,11 @@ internal DirectoryBase() { }
         public IFileSystem FileSystem { get; }
 
         /// <inheritdoc cref="Directory.CreateDirectory(string)"/>
-        public abstract DirectoryInfoBase CreateDirectory(string path);
+        public abstract IDirectoryInfo CreateDirectory(string path);
 
 #if NET40
         /// <inheritdoc cref="Directory.CreateDirectory(string,DirectorySecurity)"/>
-        public abstract DirectoryInfoBase CreateDirectory(string path, DirectorySecurity directorySecurity);
+        public abstract IDirectoryInfo CreateDirectory(string path, DirectorySecurity directorySecurity);
 #endif
 
         /// <inheritdoc cref="Directory.Delete(string)"/>
@@ -97,7 +97,7 @@ internal DirectoryBase() { }
 #endif
 
         /// <inheritdoc cref="Directory.GetParent"/>
-        public abstract DirectoryInfoBase GetParent(string path);
+        public abstract IDirectoryInfo GetParent(string path);
 
         /// <inheritdoc cref="Directory.Move"/>
         public abstract void Move(string sourceDirName, string destDirName);
@@ -127,13 +127,13 @@ internal DirectoryBase() { }
         public abstract void SetLastWriteTimeUtc(string path, DateTime lastWriteTimeUtc);
 
         /// <inheritdoc cref="Directory.EnumerateDirectories(string)"/>
-        public abstract IEnumerable<String> EnumerateDirectories(String path);
+        public abstract IEnumerable<string> EnumerateDirectories(string path);
 
         /// <inheritdoc cref="Directory.EnumerateDirectories(string,string)"/>
-        public abstract IEnumerable<String> EnumerateDirectories(String path, String searchPattern);
+        public abstract IEnumerable<string> EnumerateDirectories(string path, string searchPattern);
 
         /// <inheritdoc cref="Directory.EnumerateDirectories(string,string,SearchOption)"/>
-        public abstract IEnumerable<String> EnumerateDirectories(String path, String searchPattern, SearchOption searchOption);
+        public abstract IEnumerable<string> EnumerateDirectories(string path, string searchPattern, SearchOption searchOption);
 
         /// <inheritdoc cref="Directory.EnumerateFiles(string)"/>
         public abstract IEnumerable<string> EnumerateFiles(string path);
diff --git a/System.IO.Abstractions/DirectoryInfoBase.cs b/System.IO.Abstractions/DirectoryInfoBase.cs
index c5b40ea65..555d6d5db 100644
--- a/System.IO.Abstractions/DirectoryInfoBase.cs
+++ b/System.IO.Abstractions/DirectoryInfoBase.cs
@@ -5,7 +5,7 @@ namespace System.IO.Abstractions
 {
     /// <inheritdoc cref="DirectoryInfo"/>
     [Serializable]
-    public abstract class DirectoryInfoBase : FileSystemInfoBase
+    public abstract class DirectoryInfoBase : FileSystemInfoBase, IDirectoryInfo
     {
         protected DirectoryInfoBase(IFileSystem fileSystem) : base(fileSystem)
         {
@@ -17,48 +17,46 @@ internal DirectoryInfoBase() { }
         /// <inheritdoc cref="DirectoryInfo.Create()"/>
         public abstract void Create();
 #if NET40
-
         /// <inheritdoc cref="DirectoryInfo.Create(DirectorySecurity)"/>
         public abstract void Create(DirectorySecurity directorySecurity);
 #endif
 
         /// <inheritdoc cref="DirectoryInfo.CreateSubdirectory(string)"/>
-        public abstract DirectoryInfoBase CreateSubdirectory(string path);
+        public abstract IDirectoryInfo CreateSubdirectory(string path);
 #if NET40
-
         /// <inheritdoc cref="DirectoryInfo.CreateSubdirectory(string,DirectorySecurity)"/>
-        public abstract DirectoryInfoBase CreateSubdirectory(string path, DirectorySecurity directorySecurity);
+        public abstract IDirectoryInfo CreateSubdirectory(string path, DirectorySecurity directorySecurity);
 #endif
 
         /// <inheritdoc cref="DirectoryInfo.Delete(bool)"/>
         public abstract void Delete(bool recursive);
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateDirectories()"/>
-        public abstract IEnumerable<DirectoryInfoBase> EnumerateDirectories();
+        public abstract IEnumerable<IDirectoryInfo> EnumerateDirectories();
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateDirectories(string)"/>
-        public abstract IEnumerable<DirectoryInfoBase> EnumerateDirectories(string searchPattern);
+        public abstract IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern);
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateDirectories(string,SearchOption)"/>
-        public abstract IEnumerable<DirectoryInfoBase> EnumerateDirectories(string searchPattern, SearchOption searchOption);
+        public abstract IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern, SearchOption searchOption);
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateFiles()"/>
-        public abstract IEnumerable<FileInfoBase> EnumerateFiles();
+        public abstract IEnumerable<IFileInfo> EnumerateFiles();
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateFiles(string)"/>
-        public abstract IEnumerable<FileInfoBase> EnumerateFiles(string searchPattern);
+        public abstract IEnumerable<IFileInfo> EnumerateFiles(string searchPattern);
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateFiles(string,SearchOption)"/>
-        public abstract IEnumerable<FileInfoBase> EnumerateFiles(string searchPattern, SearchOption searchOption);
+        public abstract IEnumerable<IFileInfo> EnumerateFiles(string searchPattern, SearchOption searchOption);
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateFileSystemInfos()"/>
-        public abstract IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos();
+        public abstract IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos();
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateFileSystemInfos(string)"/>
-        public abstract IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos(string searchPattern);
+        public abstract IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern);
 
         /// <inheritdoc cref="DirectoryInfo.EnumerateFileSystemInfos(string,SearchOption)"/>
-        public abstract IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos(string searchPattern, SearchOption searchOption);
+        public abstract IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern, SearchOption searchOption);
 
         /// <inheritdoc cref="DirectoryInfo.GetAccessControl()"/>
         public abstract DirectorySecurity GetAccessControl();
@@ -67,31 +65,31 @@ internal DirectoryInfoBase() { }
         public abstract DirectorySecurity GetAccessControl(AccessControlSections includeSections);
 
         /// <inheritdoc cref="DirectoryInfo.GetDirectories()"/>
-        public abstract DirectoryInfoBase[] GetDirectories();
+        public abstract IDirectoryInfo[] GetDirectories();
 
         /// <inheritdoc cref="DirectoryInfo.GetDirectories(string)"/>
-        public abstract DirectoryInfoBase[] GetDirectories(string searchPattern);
+        public abstract IDirectoryInfo[] GetDirectories(string searchPattern);
 
         /// <inheritdoc cref="DirectoryInfo.GetDirectories(string,SearchOption)"/>
-        public abstract DirectoryInfoBase[] GetDirectories(string searchPattern, SearchOption searchOption);
+        public abstract IDirectoryInfo[] GetDirectories(string searchPattern, SearchOption searchOption);
 
         /// <inheritdoc cref="DirectoryInfo.GetFiles(string)"/>
-        public abstract FileInfoBase[] GetFiles();
+        public abstract IFileInfo[] GetFiles();
 
         /// <inheritdoc cref="DirectoryInfo.GetFiles(string)"/>
-        public abstract FileInfoBase[] GetFiles(string searchPattern);
+        public abstract IFileInfo[] GetFiles(string searchPattern);
 
         /// <inheritdoc cref="DirectoryInfo.GetFiles(string,SearchOption)"/>
-        public abstract FileInfoBase[] GetFiles(string searchPattern, SearchOption searchOption);
+        public abstract IFileInfo[] GetFiles(string searchPattern, SearchOption searchOption);
 
         /// <inheritdoc cref="DirectoryInfo.GetFileSystemInfos()"/>
-        public abstract FileSystemInfoBase[] GetFileSystemInfos();
+        public abstract IFileSystemInfo[] GetFileSystemInfos();
 
         /// <inheritdoc cref="DirectoryInfo.GetFileSystemInfos(string)"/>
-        public abstract FileSystemInfoBase[] GetFileSystemInfos(string searchPattern);
+        public abstract IFileSystemInfo[] GetFileSystemInfos(string searchPattern);
 
         /// <inheritdoc cref="DirectoryInfo.GetFileSystemInfos(string,SearchOption)"/>
-        public abstract FileSystemInfoBase[] GetFileSystemInfos(string searchPattern, SearchOption searchOption);
+        public abstract IFileSystemInfo[] GetFileSystemInfos(string searchPattern, SearchOption searchOption);
 
         /// <inheritdoc cref="DirectoryInfo.MoveTo"/>
         public abstract void MoveTo(string destDirName);
@@ -100,10 +98,10 @@ internal DirectoryInfoBase() { }
         public abstract void SetAccessControl(DirectorySecurity directorySecurity);
 
         /// <inheritdoc cref="DirectoryInfo.Parent"/>
-        public abstract DirectoryInfoBase Parent { get; }
+        public abstract IDirectoryInfo Parent { get; }
 
         /// <inheritdoc cref="DirectoryInfo.Root"/>
-        public abstract DirectoryInfoBase Root { get; }
+        public abstract IDirectoryInfo Root { get; }
 
         public static implicit operator DirectoryInfoBase(DirectoryInfo directoryInfo)
         {
diff --git a/System.IO.Abstractions/DirectoryInfoFactory.cs b/System.IO.Abstractions/DirectoryInfoFactory.cs
index 72e5bb161..8d1655298 100644
--- a/System.IO.Abstractions/DirectoryInfoFactory.cs
+++ b/System.IO.Abstractions/DirectoryInfoFactory.cs
@@ -10,7 +10,7 @@ public DirectoryInfoFactory(IFileSystem fileSystem)
             this.fileSystem = fileSystem;
         }
 
-        public DirectoryInfoBase FromDirectoryName(string directoryName)
+        public IDirectoryInfo FromDirectoryName(string directoryName)
         {
             var realDirectoryInfo = new DirectoryInfo(directoryName);
             return new DirectoryInfoWrapper(fileSystem, realDirectoryInfo);
diff --git a/System.IO.Abstractions/DirectoryInfoWrapper.cs b/System.IO.Abstractions/DirectoryInfoWrapper.cs
index 2fe120a22..d59c32a79 100644
--- a/System.IO.Abstractions/DirectoryInfoWrapper.cs
+++ b/System.IO.Abstractions/DirectoryInfoWrapper.cs
@@ -98,13 +98,13 @@ public override void Create(DirectorySecurity directorySecurity)
         }
 #endif
 
-        public override DirectoryInfoBase CreateSubdirectory(string path)
+        public override IDirectoryInfo CreateSubdirectory(string path)
         {
             return new DirectoryInfoWrapper(FileSystem, instance.CreateSubdirectory(path));
         }
 
 #if NET40
-        public override DirectoryInfoBase CreateSubdirectory(string path, DirectorySecurity directorySecurity)
+        public override IDirectoryInfo CreateSubdirectory(string path, DirectorySecurity directorySecurity)
         {
             return new DirectoryInfoWrapper(FileSystem, instance.CreateSubdirectory(path, directorySecurity));
         }
@@ -115,47 +115,47 @@ public override void Delete(bool recursive)
             instance.Delete(recursive);
         }
 
-        public override IEnumerable<DirectoryInfoBase> EnumerateDirectories()
+        public override IEnumerable<IDirectoryInfo> EnumerateDirectories()
         {
             return instance.EnumerateDirectories().Select(directoryInfo => new DirectoryInfoWrapper(FileSystem, directoryInfo));
         }
 
-        public override IEnumerable<DirectoryInfoBase> EnumerateDirectories(string searchPattern)
+        public override IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern)
         {
             return instance.EnumerateDirectories(searchPattern).Select(directoryInfo => new DirectoryInfoWrapper(FileSystem, directoryInfo));
         }
 
-        public override IEnumerable<DirectoryInfoBase> EnumerateDirectories(string searchPattern, SearchOption searchOption)
+        public override IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern, SearchOption searchOption)
         {
             return instance.EnumerateDirectories(searchPattern, searchOption).Select(directoryInfo => new DirectoryInfoWrapper(FileSystem, directoryInfo));
         }
 
-        public override IEnumerable<FileInfoBase> EnumerateFiles()
+        public override IEnumerable<IFileInfo> EnumerateFiles()
         {
             return instance.EnumerateFiles().Select(fileInfo => new FileInfoWrapper(FileSystem, fileInfo));
         }
 
-        public override IEnumerable<FileInfoBase> EnumerateFiles(string searchPattern)
+        public override IEnumerable<IFileInfo> EnumerateFiles(string searchPattern)
         {
             return instance.EnumerateFiles(searchPattern).Select(fileInfo => new FileInfoWrapper(FileSystem, fileInfo));
         }
 
-        public override IEnumerable<FileInfoBase> EnumerateFiles(string searchPattern, SearchOption searchOption)
+        public override IEnumerable<IFileInfo> EnumerateFiles(string searchPattern, SearchOption searchOption)
         {
             return instance.EnumerateFiles(searchPattern, searchOption).Select(fileInfo => new FileInfoWrapper(FileSystem, fileInfo));
         }
 
-        public override IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos()
+        public override IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos()
         {
             return instance.EnumerateFileSystemInfos().WrapFileSystemInfos(FileSystem);
         }
 
-        public override IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos(string searchPattern)
+        public override IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern)
         {
             return instance.EnumerateFileSystemInfos(searchPattern).WrapFileSystemInfos(FileSystem);
         }
 
-        public override IEnumerable<FileSystemInfoBase> EnumerateFileSystemInfos(string searchPattern, SearchOption searchOption)
+        public override IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern, SearchOption searchOption)
         {
             return instance.EnumerateFileSystemInfos(searchPattern, searchOption).WrapFileSystemInfos(FileSystem);
         }
@@ -170,47 +170,47 @@ public override DirectorySecurity GetAccessControl(AccessControlSections include
             return instance.GetAccessControl(includeSections);
         }
 
-        public override DirectoryInfoBase[] GetDirectories()
+        public override IDirectoryInfo[] GetDirectories()
         {
             return instance.GetDirectories().WrapDirectories(FileSystem);
         }
 
-        public override DirectoryInfoBase[] GetDirectories(string searchPattern)
+        public override IDirectoryInfo[] GetDirectories(string searchPattern)
         {
             return instance.GetDirectories(searchPattern).WrapDirectories(FileSystem);
         }
 
-        public override DirectoryInfoBase[] GetDirectories(string searchPattern, SearchOption searchOption)
+        public override IDirectoryInfo[] GetDirectories(string searchPattern, SearchOption searchOption)
         {
             return instance.GetDirectories(searchPattern, searchOption).WrapDirectories(FileSystem);
         }
 
-        public override FileInfoBase[] GetFiles()
+        public override IFileInfo[] GetFiles()
         {
             return instance.GetFiles().WrapFiles(FileSystem);
         }
 
-        public override FileInfoBase[] GetFiles(string searchPattern)
+        public override IFileInfo[] GetFiles(string searchPattern)
         {
             return instance.GetFiles(searchPattern).WrapFiles(FileSystem);
         }
 
-        public override FileInfoBase[] GetFiles(string searchPattern, SearchOption searchOption)
+        public override IFileInfo[] GetFiles(string searchPattern, SearchOption searchOption)
         {
             return instance.GetFiles(searchPattern, searchOption).WrapFiles(FileSystem);
         }
 
-        public override FileSystemInfoBase[] GetFileSystemInfos()
+        public override IFileSystemInfo[] GetFileSystemInfos()
         {
             return instance.GetFileSystemInfos().WrapFileSystemInfos(FileSystem);
         }
 
-        public override FileSystemInfoBase[] GetFileSystemInfos(string searchPattern)
+        public override IFileSystemInfo[] GetFileSystemInfos(string searchPattern)
         {
             return instance.GetFileSystemInfos(searchPattern).WrapFileSystemInfos(FileSystem);
         }
 
-        public override FileSystemInfoBase[] GetFileSystemInfos(string searchPattern, SearchOption searchOption)
+        public override IFileSystemInfo[] GetFileSystemInfos(string searchPattern, SearchOption searchOption)
         {
             return instance.GetFileSystemInfos(searchPattern, searchOption).WrapFileSystemInfos(FileSystem);
         }
@@ -225,7 +225,7 @@ public override void SetAccessControl(DirectorySecurity directorySecurity)
             instance.SetAccessControl(directorySecurity);
         }
 
-        public override DirectoryInfoBase Parent
+        public override IDirectoryInfo Parent
         {
             get
             {
@@ -240,7 +240,7 @@ public override DirectoryInfoBase Parent
             }
         }
 
-        public override DirectoryInfoBase Root
+        public override IDirectoryInfo Root
         {
             get { return new DirectoryInfoWrapper(FileSystem, instance.Root); }
         }
diff --git a/System.IO.Abstractions/DirectoryWrapper.cs b/System.IO.Abstractions/DirectoryWrapper.cs
index 4f4d65d40..ffe5cda0a 100644
--- a/System.IO.Abstractions/DirectoryWrapper.cs
+++ b/System.IO.Abstractions/DirectoryWrapper.cs
@@ -10,13 +10,13 @@ public DirectoryWrapper(IFileSystem fileSystem) : base(fileSystem)
         {
         }
 
-        public override DirectoryInfoBase CreateDirectory(string path)
+        public override IDirectoryInfo CreateDirectory(string path)
         {
             return new DirectoryInfoWrapper(FileSystem, Directory.CreateDirectory(path));
         }
 
 #if NET40
-        public override DirectoryInfoBase CreateDirectory(string path, DirectorySecurity directorySecurity)
+        public override IDirectoryInfo CreateDirectory(string path, DirectorySecurity directorySecurity)
         {
             return new DirectoryInfoWrapper(FileSystem, Directory.CreateDirectory(path, directorySecurity));
         }
@@ -133,7 +133,7 @@ public override string[] GetLogicalDrives()
         }
 #endif
 
-        public override DirectoryInfoBase GetParent(string path)
+        public override IDirectoryInfo GetParent(string path)
         {
             return new DirectoryInfoWrapper(FileSystem, Directory.GetParent(path));
         }
diff --git a/System.IO.Abstractions/DriveInfoBase.cs b/System.IO.Abstractions/DriveInfoBase.cs
index 55e2463d1..7b2b7083e 100644
--- a/System.IO.Abstractions/DriveInfoBase.cs
+++ b/System.IO.Abstractions/DriveInfoBase.cs
@@ -1,7 +1,7 @@
 namespace System.IO.Abstractions
 {
     [Serializable]
-    public abstract class DriveInfoBase
+    public abstract class DriveInfoBase : IDriveInfo
     {
         protected DriveInfoBase(IFileSystem fileSystem)
         {
@@ -85,7 +85,7 @@ internal DriveInfoBase() { }
         /// Gets or sets the root directory of a drive.
         /// </summary>
         /// <value>An object that contains the root directory of the drive.</value>
-        public virtual DirectoryInfoBase RootDirectory { get; protected set; }
+        public virtual IDirectoryInfo RootDirectory { get; protected set; }
 
         /// <inheritdoc cref="DriveInfo.TotalFreeSpace"/>
         /// <summary>
diff --git a/System.IO.Abstractions/DriveInfoFactory.cs b/System.IO.Abstractions/DriveInfoFactory.cs
index aed165a1c..9603a31a9 100644
--- a/System.IO.Abstractions/DriveInfoFactory.cs
+++ b/System.IO.Abstractions/DriveInfoFactory.cs
@@ -14,7 +14,7 @@ public DriveInfoFactory(IFileSystem fileSystem)
         /// Retrieves the drive names of all logical drives on a computer.
         /// </summary>
         /// <returns>An array of type <see cref="DriveInfoBase"/> that represents the logical drives on a computer.</returns>
-        public DriveInfoBase[] GetDrives()
+        public IDriveInfo[] GetDrives()
         {
             var driveInfos = DriveInfo.GetDrives();
             var driveInfoWrappers = new DriveInfoBase[driveInfos.Length];
@@ -31,7 +31,7 @@ public DriveInfoBase[] GetDrives()
         /// Initializes a new instance of the <see cref="DriveInfoBase"/> class, which acts as a wrapper for a logical drive.
         /// </summary>
         /// <param name="driveName">A valid drive path or drive letter.</param>
-        public DriveInfoBase FromDriveName(string driveName)
+        public IDriveInfo FromDriveName(string driveName)
         {
             var realDriveInfo = new DriveInfo(driveName);
             return new DriveInfoWrapper(fileSystem, realDriveInfo);
diff --git a/System.IO.Abstractions/DriveInfoWrapper.cs b/System.IO.Abstractions/DriveInfoWrapper.cs
index 5d213cd02..dfc97b1b0 100644
--- a/System.IO.Abstractions/DriveInfoWrapper.cs
+++ b/System.IO.Abstractions/DriveInfoWrapper.cs
@@ -127,7 +127,7 @@ public override long TotalSize
         /// Gets or sets the root directory of a drive.
         /// </summary>
         /// <value>An object that contains the root directory of the drive.</value>
-        public override DirectoryInfoBase RootDirectory
+        public override IDirectoryInfo RootDirectory
         {
             get { return new DirectoryInfoWrapper(FileSystem, instance.RootDirectory); }
         }
diff --git a/System.IO.Abstractions/FileBase.cs b/System.IO.Abstractions/FileBase.cs
index 0c6626163..0716ef500 100644
--- a/System.IO.Abstractions/FileBase.cs
+++ b/System.IO.Abstractions/FileBase.cs
@@ -6,7 +6,7 @@ namespace System.IO.Abstractions
 {
     /// <inheritdoc cref="File"/>
     [Serializable]
-    public abstract class FileBase
+    public abstract class FileBase : IFile
     {
         protected FileBase(IFileSystem fileSystem)
         {
diff --git a/System.IO.Abstractions/FileInfoBase.cs b/System.IO.Abstractions/FileInfoBase.cs
index cfd1508f4..c5b01c44e 100644
--- a/System.IO.Abstractions/FileInfoBase.cs
+++ b/System.IO.Abstractions/FileInfoBase.cs
@@ -4,7 +4,7 @@ namespace System.IO.Abstractions
 {
     /// <inheritdoc cref="FileInfo"/>
     [Serializable]
-    public abstract class FileInfoBase : FileSystemInfoBase
+    public abstract class FileInfoBase : FileSystemInfoBase, IFileInfo
     {
         protected FileInfoBase(IFileSystem fileSystem) : base(fileSystem)
         {
@@ -17,10 +17,10 @@ internal FileInfoBase() { }
         public abstract StreamWriter AppendText();
 
         /// <inheritdoc cref="FileInfo.CopyTo(string)"/>
-        public abstract FileInfoBase CopyTo(string destFileName);
+        public abstract IFileInfo CopyTo(string destFileName);
 
         /// <inheritdoc cref="FileInfo.CopyTo(string,bool)"/>
-        public abstract FileInfoBase CopyTo(string destFileName, bool overwrite);
+        public abstract IFileInfo CopyTo(string destFileName, bool overwrite);
 
         /// <inheritdoc cref="FileInfo.Create"/>
         public abstract Stream Create();
@@ -65,17 +65,17 @@ internal FileInfoBase() { }
 
 #if NET40
         /// <inheritdoc cref="FileInfo.Replace(string,string)"/>
-        public abstract FileInfoBase Replace(string destinationFileName, string destinationBackupFileName);
+        public abstract IFileInfo Replace(string destinationFileName, string destinationBackupFileName);
 
         /// <inheritdoc cref="FileInfo.Replace(string,string,bool)"/>
-        public abstract FileInfoBase Replace(string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors);
+        public abstract IFileInfo Replace(string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors);
 #endif
 
         /// <inheritdoc cref="FileInfo.SetAccessControl(FileSecurity)"/>
         public abstract void SetAccessControl(FileSecurity fileSecurity);
 
         /// <inheritdoc cref="FileInfo.Directory"/>
-        public abstract DirectoryInfoBase Directory { get; }
+        public abstract IDirectoryInfo Directory { get; }
 
         /// <inheritdoc cref="FileInfo.DirectoryName"/>
         public abstract string DirectoryName { get; }
diff --git a/System.IO.Abstractions/FileInfoFactory.cs b/System.IO.Abstractions/FileInfoFactory.cs
index fcebf596f..32e372e4c 100644
--- a/System.IO.Abstractions/FileInfoFactory.cs
+++ b/System.IO.Abstractions/FileInfoFactory.cs
@@ -10,7 +10,7 @@ public FileInfoFactory(IFileSystem fileSystem)
             this.fileSystem = fileSystem;
         }
 
-        public FileInfoBase FromFileName(string fileName)
+        public IFileInfo FromFileName(string fileName)
         {
             var realFileInfo = new FileInfo(fileName);
             return new FileInfoWrapper(fileSystem, realFileInfo);
diff --git a/System.IO.Abstractions/FileInfoWrapper.cs b/System.IO.Abstractions/FileInfoWrapper.cs
index 264c2033f..bd9de53ea 100644
--- a/System.IO.Abstractions/FileInfoWrapper.cs
+++ b/System.IO.Abstractions/FileInfoWrapper.cs
@@ -89,12 +89,12 @@ public override StreamWriter AppendText()
             return instance.AppendText();
         }
 
-        public override FileInfoBase CopyTo(string destFileName)
+        public override IFileInfo CopyTo(string destFileName)
         {
             return new FileInfoWrapper(FileSystem, instance.CopyTo(destFileName));
         }
 
-        public override FileInfoBase CopyTo(string destFileName, bool overwrite)
+        public override IFileInfo CopyTo(string destFileName, bool overwrite)
         {
             return new FileInfoWrapper(FileSystem, instance.CopyTo(destFileName, overwrite));
         }
@@ -167,12 +167,12 @@ public override Stream OpenWrite()
         }
 
 #if NET40
-        public override FileInfoBase Replace(string destinationFileName, string destinationBackupFileName)
+        public override IFileInfo Replace(string destinationFileName, string destinationBackupFileName)
         {
             return new FileInfoWrapper(FileSystem, instance.Replace(destinationFileName, destinationBackupFileName));
         }
 
-        public override FileInfoBase Replace(string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors)
+        public override IFileInfo Replace(string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors)
         {
             return new FileInfoWrapper(FileSystem, instance.Replace(destinationFileName, destinationBackupFileName, ignoreMetadataErrors));
         }
@@ -183,7 +183,7 @@ public override void SetAccessControl(FileSecurity fileSecurity)
             instance.SetAccessControl(fileSecurity);
         }
 
-        public override DirectoryInfoBase Directory
+        public override IDirectoryInfo Directory
         {
             get { return new DirectoryInfoWrapper(FileSystem, instance.Directory); }
         }
diff --git a/System.IO.Abstractions/FileSystem.cs b/System.IO.Abstractions/FileSystem.cs
index 144876350..3c29b1563 100644
--- a/System.IO.Abstractions/FileSystem.cs
+++ b/System.IO.Abstractions/FileSystem.cs
@@ -15,15 +15,15 @@ public FileSystem()
             FileSystemWatcher = new FileSystemWatcherFactory();
         }
 
-        public DirectoryBase Directory { get; }
+        public IDirectory Directory { get; }
 
-        public FileBase File { get; }
+        public IFile File { get; }
 
         public IFileInfoFactory FileInfo { get; }
 
         public IFileStreamFactory FileStream { get; }
 
-        public PathBase Path { get; }
+        public IPath Path { get; }
 
         public IDirectoryInfoFactory DirectoryInfo { get; }
 
diff --git a/System.IO.Abstractions/FileSystemInfoBase.cs b/System.IO.Abstractions/FileSystemInfoBase.cs
index 586b2f726..ce9358fda 100644
--- a/System.IO.Abstractions/FileSystemInfoBase.cs
+++ b/System.IO.Abstractions/FileSystemInfoBase.cs
@@ -2,7 +2,7 @@
 {
     /// <inheritdoc cref="FileSystemInfo"/>
     [Serializable]
-    public abstract class FileSystemInfoBase
+    public abstract class FileSystemInfoBase : IFileSystemInfo
     {
         protected FileSystemInfoBase(IFileSystem fileSystem)
         {
diff --git a/System.IO.Abstractions/FileSystemWatcherBase.cs b/System.IO.Abstractions/FileSystemWatcherBase.cs
index cca10924d..5d7836c6e 100644
--- a/System.IO.Abstractions/FileSystemWatcherBase.cs
+++ b/System.IO.Abstractions/FileSystemWatcherBase.cs
@@ -1,10 +1,12 @@
-using System.ComponentModel;
+#if NET40
+using System.ComponentModel;
+#endif
 
 namespace System.IO.Abstractions
 {
     /// <inheritdoc cref="FileSystemWatcher"/>
     [Serializable]
-    public abstract class FileSystemWatcherBase : IDisposable
+    public abstract class FileSystemWatcherBase : IDisposable, IFileSystemWatcher
     {
         /// <inheritdoc cref="FileSystemWatcher.IncludeSubdirectories"/>
         public abstract bool IncludeSubdirectories { get; set; }
diff --git a/System.IO.Abstractions/FileSystemWatcherFactory.cs b/System.IO.Abstractions/FileSystemWatcherFactory.cs
index f42a37e11..c18e5c460 100644
--- a/System.IO.Abstractions/FileSystemWatcherFactory.cs
+++ b/System.IO.Abstractions/FileSystemWatcherFactory.cs
@@ -8,12 +8,12 @@ namespace System.IO.Abstractions
     [Serializable]
     public class FileSystemWatcherFactory : IFileSystemWatcherFactory
     {
-        public FileSystemWatcherBase CreateNew()
+        public IFileSystemWatcher CreateNew()
         {
             return new FileSystemWatcherWrapper();
         }
 
-        public FileSystemWatcherBase FromPath(string path)
+        public IFileSystemWatcher FromPath(string path)
         {
             return new FileSystemWatcherWrapper(path);
         }
diff --git a/System.IO.Abstractions/IDirectory.cs b/System.IO.Abstractions/IDirectory.cs
new file mode 100644
index 000000000..5e7af2826
--- /dev/null
+++ b/System.IO.Abstractions/IDirectory.cs
@@ -0,0 +1,105 @@
+using System.Collections.Generic;
+using System.Security.AccessControl;
+
+namespace System.IO.Abstractions
+{
+    public interface IDirectory
+    {
+        /// <summary>
+        /// Exposes the underlying filesystem implementation. This is useful for implementing extension methods.
+        /// </summary>
+        IFileSystem FileSystem { get; }
+
+        /// <inheritdoc cref="Directory.CreateDirectory(string)"/>
+        IDirectoryInfo CreateDirectory(string path);
+
+#if NET40
+        /// <inheritdoc cref="Directory.CreateDirectory(string,DirectorySecurity)"/>
+        IDirectoryInfo CreateDirectory(string path, DirectorySecurity directorySecurity);
+#endif
+        /// <inheritdoc cref="Directory.Delete(string)"/>
+        void Delete(string path);
+        /// <inheritdoc cref="Directory.Delete(string,bool)"/>
+        void Delete(string path, bool recursive);
+        /// <inheritdoc cref="Directory.Exists"/>
+        bool Exists(string path);
+        /// <inheritdoc cref="Directory.GetAccessControl(string)"/>
+        DirectorySecurity GetAccessControl(string path);
+        /// <inheritdoc cref="Directory.GetAccessControl(string,AccessControlSections)"/>
+        DirectorySecurity GetAccessControl(string path, AccessControlSections includeSections);
+        /// <inheritdoc cref="Directory.GetCreationTime"/>
+        DateTime GetCreationTime(string path);
+        /// <inheritdoc cref="Directory.GetCreationTimeUtc"/>
+        DateTime GetCreationTimeUtc(string path);
+        /// <inheritdoc cref="Directory.GetCurrentDirectory"/>
+        string GetCurrentDirectory();
+        /// <inheritdoc cref="Directory.GetDirectories(string)"/>
+        string[] GetDirectories(string path);
+        /// <inheritdoc cref="Directory.GetDirectories(string,string)"/>
+        string[] GetDirectories(string path, string searchPattern);
+        /// <inheritdoc cref="Directory.GetDirectories(string,string,SearchOption)"/>
+        string[] GetDirectories(string path, string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="Directory.GetDirectoryRoot"/>
+        string GetDirectoryRoot(string path);
+        /// <inheritdoc cref="Directory.GetFiles(string)"/>
+        string[] GetFiles(string path);
+        /// <inheritdoc cref="Directory.GetFiles(string,string)"/>
+        string[] GetFiles(string path, string searchPattern);
+        /// <inheritdoc cref="Directory.GetFiles(string,string,SearchOption)"/>
+        string[] GetFiles(string path, string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="Directory.GetFileSystemEntries(string)"/>
+        string[] GetFileSystemEntries(string path);
+        /// <inheritdoc cref="Directory.GetFileSystemEntries(string,string)"/>
+        string[] GetFileSystemEntries(string path, string searchPattern);
+        /// <inheritdoc cref="Directory.GetLastAccessTime"/>
+        DateTime GetLastAccessTime(string path);
+        /// <inheritdoc cref="Directory.GetLastAccessTimeUtc"/>
+        DateTime GetLastAccessTimeUtc(string path);
+        /// <inheritdoc cref="Directory.GetLastWriteTime"/>
+        DateTime GetLastWriteTime(string path);
+        /// <inheritdoc cref="Directory.GetLastWriteTimeUtc"/>
+        DateTime GetLastWriteTimeUtc(string path);
+#if NET40
+        /// <inheritdoc cref="Directory.GetLogicalDrives"/>
+        string[] GetLogicalDrives();
+#endif
+        /// <inheritdoc cref="Directory.GetParent"/>
+        IDirectoryInfo GetParent(string path);
+        /// <inheritdoc cref="Directory.Move"/>
+        void Move(string sourceDirName, string destDirName);
+        /// <inheritdoc cref="Directory.SetAccessControl"/>
+        void SetAccessControl(string path, DirectorySecurity directorySecurity);
+        /// <inheritdoc cref="Directory.SetCreationTime"/>
+        void SetCreationTime(string path, DateTime creationTime);
+        /// <inheritdoc cref="Directory.SetCreationTimeUtc"/>
+        void SetCreationTimeUtc(string path, DateTime creationTimeUtc);
+        /// <inheritdoc cref="Directory.SetCurrentDirectory"/>
+        void SetCurrentDirectory(string path);
+        /// <inheritdoc cref="Directory.SetLastAccessTime"/>
+        void SetLastAccessTime(string path, DateTime lastAccessTime);
+        /// <inheritdoc cref="Directory.SetLastAccessTimeUtc"/>
+        void SetLastAccessTimeUtc(string path, DateTime lastAccessTimeUtc);
+        /// <inheritdoc cref="Directory.SetLastWriteTime"/>
+        void SetLastWriteTime(string path, DateTime lastWriteTime);
+        /// <inheritdoc cref="Directory.SetLastWriteTimeUtc"/>
+        void SetLastWriteTimeUtc(string path, DateTime lastWriteTimeUtc);
+        /// <inheritdoc cref="Directory.EnumerateDirectories(string)"/>
+        IEnumerable<string> EnumerateDirectories(string path);
+        /// <inheritdoc cref="Directory.EnumerateDirectories(string,string)"/>
+        IEnumerable<string> EnumerateDirectories(string path, string searchPattern);
+        /// <inheritdoc cref="Directory.EnumerateDirectories(string,string,SearchOption)"/>
+        IEnumerable<string> EnumerateDirectories(string path, string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="Directory.EnumerateFiles(string)"/>
+        IEnumerable<string> EnumerateFiles(string path);
+        /// <inheritdoc cref="Directory.EnumerateFiles(string,string)"/>
+        IEnumerable<string> EnumerateFiles(string path, string searchPattern);
+        /// <inheritdoc cref="Directory.EnumerateFiles(string,string,SearchOption)"/>
+        IEnumerable<string> EnumerateFiles(string path, string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="Directory.EnumerateFileSystemEntries(string)"/>
+        IEnumerable<string> EnumerateFileSystemEntries(string path);
+        /// <inheritdoc cref="Directory.EnumerateFileSystemEntries(string,string)"/>
+        IEnumerable<string> EnumerateFileSystemEntries(string path, string searchPattern);
+        /// <inheritdoc cref="Directory.EnumerateFileSystemEntries(string,string,SearchOption)"/>
+        IEnumerable<string> EnumerateFileSystemEntries(string path, string searchPattern, SearchOption searchOption);
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/IDirectoryInfo.cs b/System.IO.Abstractions/IDirectoryInfo.cs
new file mode 100644
index 000000000..434b38778
--- /dev/null
+++ b/System.IO.Abstractions/IDirectoryInfo.cs
@@ -0,0 +1,71 @@
+using System.Collections.Generic;
+using System.Security.AccessControl;
+
+namespace System.IO.Abstractions
+{
+    public interface IDirectoryInfo: IFileSystemInfo
+    {
+        /// <inheritdoc cref="DirectoryInfo.Create()"/>
+        void Create();
+#if NET40
+        /// <inheritdoc cref="DirectoryInfo.Create(DirectorySecurity)"/>
+        void Create(DirectorySecurity directorySecurity);
+#endif
+        /// <inheritdoc cref="DirectoryInfo.CreateSubdirectory(string)"/>
+        IDirectoryInfo CreateSubdirectory(string path);
+#if NET40
+        /// <inheritdoc cref="DirectoryInfo.CreateSubdirectory(string,DirectorySecurity)"/>
+        IDirectoryInfo CreateSubdirectory(string path, DirectorySecurity directorySecurity);
+#endif
+        /// <inheritdoc cref="DirectoryInfo.Delete(bool)"/>
+        void Delete(bool recursive);
+        /// <inheritdoc cref="DirectoryInfo.EnumerateDirectories()"/>
+        IEnumerable<IDirectoryInfo> EnumerateDirectories();
+        /// <inheritdoc cref="DirectoryInfo.EnumerateDirectories(string)"/>
+        IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern);
+        /// <inheritdoc cref="DirectoryInfo.EnumerateDirectories(string,SearchOption)"/>
+        IEnumerable<IDirectoryInfo> EnumerateDirectories(string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="DirectoryInfo.EnumerateFiles()"/>
+        IEnumerable<IFileInfo> EnumerateFiles();
+        /// <inheritdoc cref="DirectoryInfo.EnumerateFiles(string)"/>
+        IEnumerable<IFileInfo> EnumerateFiles(string searchPattern);
+        /// <inheritdoc cref="DirectoryInfo.EnumerateFiles(string,SearchOption)"/>
+        IEnumerable<IFileInfo> EnumerateFiles(string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="DirectoryInfo.EnumerateFileSystemInfos()"/>
+        IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos();
+        /// <inheritdoc cref="DirectoryInfo.EnumerateFileSystemInfos(string)"/>
+        IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern);
+        /// <inheritdoc cref="DirectoryInfo.EnumerateFileSystemInfos(string,SearchOption)"/>
+        IEnumerable<IFileSystemInfo> EnumerateFileSystemInfos(string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="DirectoryInfo.GetAccessControl()"/>
+        DirectorySecurity GetAccessControl();
+        /// <inheritdoc cref="DirectoryInfo.GetAccessControl(AccessControlSections)"/>
+        DirectorySecurity GetAccessControl(AccessControlSections includeSections);
+        /// <inheritdoc cref="DirectoryInfo.GetDirectories()"/>
+        IDirectoryInfo[] GetDirectories();
+        /// <inheritdoc cref="DirectoryInfo.GetDirectories(string)"/>
+        IDirectoryInfo[] GetDirectories(string searchPattern);
+        /// <inheritdoc cref="DirectoryInfo.GetDirectories(string,SearchOption)"/>
+        IDirectoryInfo[] GetDirectories(string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="DirectoryInfo.GetFiles(string)"/>
+        IFileInfo[] GetFiles();
+        /// <inheritdoc cref="DirectoryInfo.GetFiles(string)"/>
+        IFileInfo[] GetFiles(string searchPattern);
+        /// <inheritdoc cref="DirectoryInfo.GetFiles(string,SearchOption)"/>
+        IFileInfo[] GetFiles(string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="DirectoryInfo.GetFileSystemInfos()"/>
+        IFileSystemInfo[] GetFileSystemInfos();
+        /// <inheritdoc cref="DirectoryInfo.GetFileSystemInfos(string)"/>
+        IFileSystemInfo[] GetFileSystemInfos(string searchPattern);
+        /// <inheritdoc cref="DirectoryInfo.GetFileSystemInfos(string,SearchOption)"/>
+        IFileSystemInfo[] GetFileSystemInfos(string searchPattern, SearchOption searchOption);
+        /// <inheritdoc cref="DirectoryInfo.MoveTo"/>
+        void MoveTo(string destDirName);
+        /// <inheritdoc cref="DirectoryInfo.SetAccessControl"/>
+        void SetAccessControl(DirectorySecurity directorySecurity);
+        /// <inheritdoc cref="DirectoryInfo.Parent"/>
+        IDirectoryInfo Parent { get; }
+        /// <inheritdoc cref="DirectoryInfo.Root"/>
+        IDirectoryInfo Root { get; }
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/IDirectoryInfoFactory.cs b/System.IO.Abstractions/IDirectoryInfoFactory.cs
index 9f6e9e32e..acc575965 100644
--- a/System.IO.Abstractions/IDirectoryInfoFactory.cs
+++ b/System.IO.Abstractions/IDirectoryInfoFactory.cs
@@ -6,6 +6,6 @@ public interface IDirectoryInfoFactory
         /// Initializes a new instance of the <see cref="DirectoryInfoBase"/> class, which acts as a wrapper for a directory path.
         /// </summary>
         /// <param name="directoryName">The fully qualified name of the new directory, or the relative directory name.</param>
-        DirectoryInfoBase FromDirectoryName(string directoryName);
+        IDirectoryInfo FromDirectoryName(string directoryName);
     }
 }
\ No newline at end of file
diff --git a/System.IO.Abstractions/IDriveInfo.cs b/System.IO.Abstractions/IDriveInfo.cs
new file mode 100644
index 000000000..356c1a845
--- /dev/null
+++ b/System.IO.Abstractions/IDriveInfo.cs
@@ -0,0 +1,28 @@
+namespace System.IO.Abstractions
+{
+    public interface IDriveInfo
+    {
+        /// <summary>
+        /// Exposes the underlying filesystem implementation. This is useful for implementing extension methods.
+        /// </summary>
+        IFileSystem FileSystem { get; }
+        /// <inheritdoc cref="DriveInfo.AvailableFreeSpace"/>
+        long AvailableFreeSpace { get; }
+        /// <inheritdoc cref="DriveInfo.DriveFormat"/>
+        string DriveFormat { get; }
+        /// <inheritdoc cref="DriveInfo.DriveType"/>
+        DriveType DriveType { get; }
+        /// <inheritdoc cref="DriveInfo.IsReady"/>
+        bool IsReady { get; }
+        /// <inheritdoc cref="DriveInfo.Name"/>
+        string Name { get; }
+        /// <inheritdoc cref="DriveInfo.RootDirectory"/>
+        IDirectoryInfo RootDirectory { get; }
+        /// <inheritdoc cref="DriveInfo.TotalFreeSpace"/>
+        long TotalFreeSpace { get; }
+        /// <inheritdoc cref="DriveInfo.TotalSize"/>
+        long TotalSize { get; }
+        /// <inheritdoc cref="DriveInfo.VolumeLabel"/>
+        string VolumeLabel { get; set; }
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/IDriveInfoFactory.cs b/System.IO.Abstractions/IDriveInfoFactory.cs
index 53c3bb2b3..7a2cca36a 100644
--- a/System.IO.Abstractions/IDriveInfoFactory.cs
+++ b/System.IO.Abstractions/IDriveInfoFactory.cs
@@ -9,12 +9,12 @@ public interface IDriveInfoFactory
         /// Retrieves the drive names of all logical drives on a computer.
         /// </summary>
         /// <returns>An array of type <see cref="DriveInfoBase"/> that represents the logical drives on a computer.</returns>
-        DriveInfoBase[] GetDrives();
+        IDriveInfo[] GetDrives();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DriveInfoBase"/> class, which acts as a wrapper for a logical drive.
         /// </summary>
         /// <param name="driveName">A valid drive path or drive letter.</param>
-        DriveInfoBase FromDriveName(string driveName);
+        IDriveInfo FromDriveName(string driveName);
     }
 }
diff --git a/System.IO.Abstractions/IFile.cs b/System.IO.Abstractions/IFile.cs
new file mode 100644
index 000000000..169add2c2
--- /dev/null
+++ b/System.IO.Abstractions/IFile.cs
@@ -0,0 +1,135 @@
+using System.Collections.Generic;
+using System.Security.AccessControl;
+using System.Text;
+
+namespace System.IO.Abstractions
+{
+    public interface IFile
+    {
+        /// <summary>
+        /// Exposes the underlying filesystem implementation. This is useful for implementing extension methods.
+        /// </summary>
+        IFileSystem FileSystem { get; }
+
+        /// <inheritdoc cref="File.AppendAllLines(string,IEnumerable{string})"/>
+        void AppendAllLines(string path, IEnumerable<string> contents);
+        /// <inheritdoc cref="File.AppendAllLines(string,IEnumerable{string},Encoding)"/>
+        void AppendAllLines(string path, IEnumerable<string> contents, Encoding encoding);
+        /// <inheritdoc cref="File.AppendAllText(string,string)"/>
+        void AppendAllText(string path, string contents);
+        /// <inheritdoc cref="File.AppendAllText(string,string,Encoding)"/>
+        void AppendAllText(string path, string contents, Encoding encoding);
+        /// <inheritdoc cref="File.AppendText"/>
+        StreamWriter AppendText(string path);
+        /// <inheritdoc cref="File.Copy(string,string)"/>
+        void Copy(string sourceFileName, string destFileName);
+        /// <inheritdoc cref="File.Copy(string,string,bool)"/>
+        void Copy(string sourceFileName, string destFileName, bool overwrite);
+        /// <inheritdoc cref="File.Create(string)"/>
+        Stream Create(string path);
+        /// <inheritdoc cref="File.Create(string,int)"/>
+        Stream Create(string path, int bufferSize);
+        /// <inheritdoc cref="File.Create(string,int,FileOptions)"/>
+        Stream Create(string path, int bufferSize, FileOptions options);
+#if NET40
+        /// <inheritdoc cref="File.Create(string,int,FileOptions,FileSecurity)"/>
+        Stream Create(string path, int bufferSize, FileOptions options, FileSecurity fileSecurity);
+#endif
+        /// <inheritdoc cref="File.CreateText"/>
+        StreamWriter CreateText(string path);
+#if NET40
+        /// <inheritdoc cref="File.Decrypt"/>
+        void Decrypt(string path);
+#endif
+        /// <inheritdoc cref="File.Delete"/>
+        void Delete(string path);
+#if NET40
+        /// <inheritdoc cref="File.Encrypt"/>
+        void Encrypt(string path);
+#endif
+        /// <inheritdoc cref="File.Exists"/>
+        bool Exists(string path);
+        /// <inheritdoc cref="File.GetAccessControl(string)"/>
+        FileSecurity GetAccessControl(string path);
+        /// <inheritdoc cref="File.GetAccessControl(string,AccessControlSections)"/>
+        FileSecurity GetAccessControl(string path, AccessControlSections includeSections);
+        /// <inheritdoc cref="File.GetAttributes"/>
+        FileAttributes GetAttributes(string path);
+        /// <inheritdoc cref="File.GetCreationTime"/>
+        DateTime GetCreationTime(string path);
+        /// <inheritdoc cref="File.GetCreationTimeUtc"/>
+        DateTime GetCreationTimeUtc(string path);
+        /// <inheritdoc cref="File.GetLastAccessTime"/>
+        DateTime GetLastAccessTime(string path);
+        /// <inheritdoc cref="File.GetLastAccessTimeUtc"/>
+        DateTime GetLastAccessTimeUtc(string path);
+        /// <inheritdoc cref="File.GetLastWriteTime"/>
+        DateTime GetLastWriteTime(string path);
+        /// <inheritdoc cref="File.GetLastWriteTimeUtc"/>
+        DateTime GetLastWriteTimeUtc(string path);
+        /// <inheritdoc cref="File.Move"/>
+        void Move(string sourceFileName, string destFileName);
+        /// <inheritdoc cref="File.Open(string,FileMode)"/>
+        Stream Open(string path, FileMode mode);
+        /// <inheritdoc cref="File.Open(string,FileMode,FileAccess)"/>
+        Stream Open(string path, FileMode mode, FileAccess access);
+        /// <inheritdoc cref="File.Open(string,FileMode,FileAccess,FileShare)"/>
+        Stream Open(string path, FileMode mode, FileAccess access, FileShare share);
+        /// <inheritdoc cref="File.OpenRead"/>
+        Stream OpenRead(string path);
+        /// <inheritdoc cref="File.OpenText"/>
+        StreamReader OpenText(string path);
+        /// <inheritdoc cref="File.OpenWrite"/>
+        Stream OpenWrite(string path);
+        /// <inheritdoc cref="File.ReadAllBytes"/>
+        byte[] ReadAllBytes(string path);
+        /// <inheritdoc cref="File.ReadAllLines(string)"/>
+        string[] ReadAllLines(string path);
+        /// <inheritdoc cref="File.ReadAllLines(string,Encoding)"/>
+        string[] ReadAllLines(string path, Encoding encoding);
+        /// <inheritdoc cref="File.ReadAllText(string)"/>
+        string ReadAllText(string path);
+        /// <inheritdoc cref="File.ReadAllText(string,Encoding)"/>
+        string ReadAllText(string path, Encoding encoding);
+        /// <inheritdoc cref="File.ReadLines(string)"/>
+        IEnumerable<string> ReadLines(string path);
+        /// <inheritdoc cref="File.ReadLines(string,Encoding)"/>
+        IEnumerable<string> ReadLines(string path, Encoding encoding);
+#if NET40
+        /// <inheritdoc cref="File.Replace(string,string,string)"/>
+        void Replace(string sourceFileName, string destinationFileName, string destinationBackupFileName);
+        /// <inheritdoc cref="File.Replace(string,string,string,bool)"/>
+        void Replace(string sourceFileName, string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors);
+#endif
+        /// <inheritdoc cref="File.SetAccessControl(string,FileSecurity)"/>
+        void SetAccessControl(string path, FileSecurity fileSecurity);
+        /// <inheritdoc cref="File.SetAttributes"/>
+        void SetAttributes(string path, FileAttributes fileAttributes);
+        /// <inheritdoc cref="File.SetCreationTime"/>
+        void SetCreationTime(string path, DateTime creationTime);
+        /// <inheritdoc cref="File.SetCreationTimeUtc"/>
+        void SetCreationTimeUtc(string path, DateTime creationTimeUtc);
+        /// <inheritdoc cref="File.SetLastAccessTime"/>
+        void SetLastAccessTime(string path, DateTime lastAccessTime);
+        /// <inheritdoc cref="File.SetLastAccessTimeUtc"/>
+        void SetLastAccessTimeUtc(string path, DateTime lastAccessTimeUtc);
+        /// <inheritdoc cref="File.SetLastWriteTime"/>
+        void SetLastWriteTime(string path, DateTime lastWriteTime);
+        /// <inheritdoc cref="File.SetLastWriteTimeUtc"/>
+        void SetLastWriteTimeUtc(string path, DateTime lastWriteTimeUtc);
+        /// <inheritdoc cref="File.WriteAllBytes"/>
+        void WriteAllBytes(string path, byte[] bytes);
+        /// <inheritdoc cref="File.WriteAllLines(string,IEnumerable{string})"/>
+        void WriteAllLines(string path, IEnumerable<string> contents);
+        /// <inheritdoc cref="File.WriteAllLines(string,IEnumerable{string},Encoding)"/>
+        void WriteAllLines(string path, IEnumerable<string> contents, Encoding encoding);
+        /// <inheritdoc cref="File.WriteAllLines(string,string[])"/>
+        void WriteAllLines(string path, string[] contents);
+        /// <inheritdoc cref="File.WriteAllLines(string,string[],Encoding)"/>
+        void WriteAllLines(string path, string[] contents, Encoding encoding);
+        /// <inheritdoc cref="File.WriteAllText(string,string)"/>
+        void WriteAllText(string path, string contents);
+        /// <inheritdoc cref="File.WriteAllText(string,string,Encoding)"/>
+        void WriteAllText(string path, string contents, Encoding encoding);
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/IFileInfo.cs b/System.IO.Abstractions/IFileInfo.cs
new file mode 100644
index 000000000..184b9ac11
--- /dev/null
+++ b/System.IO.Abstractions/IFileInfo.cs
@@ -0,0 +1,58 @@
+using System.Security.AccessControl;
+
+namespace System.IO.Abstractions
+{
+    public interface IFileInfo: IFileSystemInfo
+    {
+        /// <inheritdoc cref="FileInfo.AppendText"/>
+        StreamWriter AppendText();
+        /// <inheritdoc cref="FileInfo.CopyTo(string)"/>
+        IFileInfo CopyTo(string destFileName);
+        /// <inheritdoc cref="FileInfo.CopyTo(string,bool)"/>
+        IFileInfo CopyTo(string destFileName, bool overwrite);
+        /// <inheritdoc cref="FileInfo.Create"/>
+        Stream Create();
+        /// <inheritdoc cref="FileInfo.CreateText"/>
+        StreamWriter CreateText();
+#if NET40
+        /// <inheritdoc cref="FileInfo.Decrypt"/>
+        void Decrypt();
+        /// <inheritdoc cref="FileInfo.Encrypt"/>
+        void Encrypt();
+#endif
+        /// <inheritdoc cref="FileInfo.GetAccessControl()"/>
+        FileSecurity GetAccessControl();
+        /// <inheritdoc cref="FileInfo.GetAccessControl(AccessControlSections)"/>
+        FileSecurity GetAccessControl(AccessControlSections includeSections);
+        /// <inheritdoc cref="FileInfo.MoveTo"/>
+        void MoveTo(string destFileName);
+        /// <inheritdoc cref="FileInfo.Open(FileMode)"/>
+        Stream Open(FileMode mode);
+        /// <inheritdoc cref="FileInfo.Open(FileMode,FileAccess)"/>
+        Stream Open(FileMode mode, FileAccess access);
+        /// <inheritdoc cref="FileInfo.Open(FileMode,FileAccess,FileShare)"/>
+        Stream Open(FileMode mode, FileAccess access, FileShare share);
+        /// <inheritdoc cref="FileInfo.OpenRead"/>
+        Stream OpenRead();
+        /// <inheritdoc cref="FileInfo.OpenText"/>
+        StreamReader OpenText();
+        /// <inheritdoc cref="FileInfo.OpenWrite"/>
+        Stream OpenWrite();
+#if NET40
+        /// <inheritdoc cref="FileInfo.Replace(string,string)"/>
+        IFileInfo Replace(string destinationFileName, string destinationBackupFileName);
+        /// <inheritdoc cref="FileInfo.Replace(string,string,bool)"/>
+        IFileInfo Replace(string destinationFileName, string destinationBackupFileName, bool ignoreMetadataErrors);
+#endif
+        /// <inheritdoc cref="FileInfo.SetAccessControl(FileSecurity)"/>
+        void SetAccessControl(FileSecurity fileSecurity);
+        /// <inheritdoc cref="FileInfo.Directory"/>
+        IDirectoryInfo Directory { get; }
+        /// <inheritdoc cref="FileInfo.DirectoryName"/>
+        string DirectoryName { get; }
+        /// <inheritdoc cref="FileInfo.IsReadOnly"/>
+        bool IsReadOnly { get; set; }
+        /// <inheritdoc cref="FileInfo.Length"/>
+        long Length { get; }
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/IFileInfoFactory.cs b/System.IO.Abstractions/IFileInfoFactory.cs
index aeeeded04..f371f1087 100644
--- a/System.IO.Abstractions/IFileInfoFactory.cs
+++ b/System.IO.Abstractions/IFileInfoFactory.cs
@@ -6,6 +6,6 @@ public interface IFileInfoFactory
         /// Initializes a new instance of the <see cref="FileInfoBase"/> class, which acts as a wrapper for a file path.
         /// </summary>
         /// <param name="fileName">The fully qualified name of the new file, or the relative file name.</param>
-        FileInfoBase FromFileName(string fileName);
+        IFileInfo FromFileName(string fileName);
     }
 }
\ No newline at end of file
diff --git a/System.IO.Abstractions/IFileSystem.cs b/System.IO.Abstractions/IFileSystem.cs
index 32472125e..48ad19b07 100644
--- a/System.IO.Abstractions/IFileSystem.cs
+++ b/System.IO.Abstractions/IFileSystem.cs
@@ -2,11 +2,11 @@
 {
     public interface IFileSystem
     {
-        FileBase File { get; }
-        DirectoryBase Directory { get; }
+        IFile File { get; }
+        IDirectory Directory { get; }
         IFileInfoFactory FileInfo { get; }
         IFileStreamFactory FileStream { get; }
-        PathBase Path { get; }
+        IPath Path { get; }
         IDirectoryInfoFactory DirectoryInfo { get; }
         IDriveInfoFactory DriveInfo { get; }
         IFileSystemWatcherFactory FileSystemWatcher { get; }
diff --git a/System.IO.Abstractions/IFileSystemInfo.cs b/System.IO.Abstractions/IFileSystemInfo.cs
new file mode 100644
index 000000000..9331ad04c
--- /dev/null
+++ b/System.IO.Abstractions/IFileSystemInfo.cs
@@ -0,0 +1,36 @@
+namespace System.IO.Abstractions
+{
+    public interface IFileSystemInfo
+    {
+        /// <summary>
+        /// Exposes the underlying filesystem implementation. This is useful for implementing extension methods.
+        /// </summary>
+        IFileSystem FileSystem { get; }
+        /// <inheritdoc cref="FileSystemInfo.Delete"/>
+        void Delete();
+        /// <inheritdoc cref="FileSystemInfo.Refresh"/>
+        void Refresh();
+        /// <inheritdoc cref="FileSystemInfo.Attributes"/>
+        FileAttributes Attributes { get; set; }
+        /// <inheritdoc cref="FileSystemInfo.CreationTime"/>
+        DateTime CreationTime { get; set; }
+        /// <inheritdoc cref="FileSystemInfo.CreationTimeUtc"/>
+        DateTime CreationTimeUtc { get; set; }
+        /// <inheritdoc cref="FileSystemInfo.Exists"/>
+        bool Exists { get; }
+        /// <inheritdoc cref="FileSystemInfo.Extension"/>
+        string Extension { get; }
+        /// <inheritdoc cref="FileSystemInfo.FullName"/>
+        string FullName { get; }
+        /// <inheritdoc cref="FileSystemInfo.LastAccessTime"/>
+        DateTime LastAccessTime { get; set; }
+        /// <inheritdoc cref="FileSystemInfo.LastAccessTimeUtc"/>
+        DateTime LastAccessTimeUtc { get; set; }
+        /// <inheritdoc cref="FileSystemInfo.LastWriteTime"/>
+        DateTime LastWriteTime { get; set; }
+        /// <inheritdoc cref="FileSystemInfo.LastWriteTimeUtc"/>
+        DateTime LastWriteTimeUtc { get; set; }
+        /// <inheritdoc cref="FileSystemInfo.Name"/>
+        string Name { get; }
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/IFileSystemWatcher.cs b/System.IO.Abstractions/IFileSystemWatcher.cs
new file mode 100644
index 000000000..8faae96c9
--- /dev/null
+++ b/System.IO.Abstractions/IFileSystemWatcher.cs
@@ -0,0 +1,50 @@
+#if NET40
+using System.ComponentModel;
+#endif
+
+namespace System.IO.Abstractions
+{
+    public interface IFileSystemWatcher
+    {
+        /// <inheritdoc cref="FileSystemWatcher.IncludeSubdirectories"/>
+        bool IncludeSubdirectories { get; set; }
+        /// <inheritdoc cref="FileSystemWatcher.EnableRaisingEvents"/>
+        bool EnableRaisingEvents { get; set; }
+        /// <inheritdoc cref="FileSystemWatcher.Filter"/>
+        string Filter { get; set; }
+        /// <inheritdoc cref="FileSystemWatcher.InternalBufferSize"/>
+        int InternalBufferSize { get; set; }
+        /// <inheritdoc cref="FileSystemWatcher.NotifyFilter"/>
+        NotifyFilters NotifyFilter { get; set; }
+        /// <inheritdoc cref="FileSystemWatcher.Path"/>
+        string Path { get; set; }
+#if NET40
+        /// <inheritdoc cref="FileSystemWatcher.Site"/>
+        ISite Site { get; set; }
+        /// <inheritdoc cref="FileSystemWatcher.SynchronizingObject"/>
+        ISynchronizeInvoke SynchronizingObject { get; set; }
+#endif
+        /// <inheritdoc cref="FileSystemWatcher.Changed"/>
+        event FileSystemEventHandler Changed;
+        /// <inheritdoc cref="FileSystemWatcher.Created"/>
+        event FileSystemEventHandler Created;
+        /// <inheritdoc cref="FileSystemWatcher.Deleted"/>
+        event FileSystemEventHandler Deleted;
+        /// <inheritdoc cref="FileSystemWatcher.Error"/>
+        event ErrorEventHandler Error;
+        /// <inheritdoc cref="FileSystemWatcher.Renamed"/>
+        event RenamedEventHandler Renamed;
+#if NET40
+        /// <inheritdoc cref="FileSystemWatcher.BeginInit"/>
+        void BeginInit();
+#endif
+#if NET40
+        /// <inheritdoc cref="FileSystemWatcher.EndInit"/>
+        void EndInit();
+#endif
+        /// <inheritdoc cref="FileSystemWatcher.WaitForChanged(WatcherChangeTypes)"/>
+        WaitForChangedResult WaitForChanged(WatcherChangeTypes changeType);
+        /// <inheritdoc cref="FileSystemWatcher.WaitForChanged(WatcherChangeTypes,int)"/>
+        WaitForChangedResult WaitForChanged(WatcherChangeTypes changeType, int timeout);
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/IFileSystemWatcherFactory.cs b/System.IO.Abstractions/IFileSystemWatcherFactory.cs
index b947c93a5..e9612b206 100644
--- a/System.IO.Abstractions/IFileSystemWatcherFactory.cs
+++ b/System.IO.Abstractions/IFileSystemWatcherFactory.cs
@@ -11,13 +11,13 @@ public interface IFileSystemWatcherFactory
         /// Initializes a new instance of the <see cref="FileSystemWatcherBase"/> class, which acts as a wrapper for a FileSystemWatcher
         /// </summary>
         /// <returns></returns>
-        FileSystemWatcherBase CreateNew();
+        IFileSystemWatcher CreateNew();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="FileSystemWatcherBase"/> class, which acts as a wrapper for a FileSystemWatcher
         /// </summary>
         /// <param name="path">Path to generate the FileSystemWatcherBase for</param>
         /// <returns></returns>
-        FileSystemWatcherBase FromPath(string path);
+        IFileSystemWatcher FromPath(string path);
     }
 }
diff --git a/System.IO.Abstractions/IPath.cs b/System.IO.Abstractions/IPath.cs
new file mode 100644
index 000000000..3f694f045
--- /dev/null
+++ b/System.IO.Abstractions/IPath.cs
@@ -0,0 +1,55 @@
+namespace System.IO.Abstractions
+{
+    public interface IPath
+    {
+        /// <inheritdoc cref="Path.AltDirectorySeparatorChar"/>
+        char AltDirectorySeparatorChar { get; }
+        /// <inheritdoc cref="Path.DirectorySeparatorChar"/>
+        char DirectorySeparatorChar { get; }
+        /// <summary>
+        /// Exposes the underlying filesystem implementation. This is useful for implementing extension methods.
+        /// </summary>
+        IFileSystem FileSystem { get; }
+        /// <inheritdoc cref="Path.PathSeparator"/>
+        char PathSeparator { get; }
+        /// <inheritdoc cref="Path.VolumeSeparatorChar"/>
+        char VolumeSeparatorChar { get; }
+
+        /// <inheritdoc cref="Path.ChangeExtension"/>
+        string ChangeExtension(string path, string extension);
+        /// <inheritdoc cref="Path.Combine(string[])"/>
+        string Combine(params string[] paths);
+        /// <inheritdoc cref="Path.Combine(string,string)"/>
+        string Combine(string path1, string path2);
+        /// <inheritdoc cref="Path.Combine(string,string,string)"/>
+        string Combine(string path1, string path2, string path3);
+        /// <inheritdoc cref="Path.Combine(string,string,string,string)"/>
+        string Combine(string path1, string path2, string path3, string path4);
+        /// <inheritdoc cref="Path.GetDirectoryName"/>
+        string GetDirectoryName(string path);
+        /// <inheritdoc cref="Path.GetExtension"/>
+        string GetExtension(string path);
+        /// <inheritdoc cref="Path.GetFileName"/>
+        string GetFileName(string path);
+        /// <inheritdoc cref="Path.GetFileNameWithoutExtension"/>
+        string GetFileNameWithoutExtension(string path);
+        /// <inheritdoc cref="Path.GetFullPath"/>
+        string GetFullPath(string path);
+        /// <inheritdoc cref="Path.GetInvalidFileNameChars"/>
+        char[] GetInvalidFileNameChars();
+        /// <inheritdoc cref="Path.GetInvalidPathChars"/>
+        char[] GetInvalidPathChars();
+        /// <inheritdoc cref="Path.GetPathRoot"/>
+        string GetPathRoot(string path);
+        /// <inheritdoc cref="Path.GetRandomFileName"/>
+        string GetRandomFileName();
+        /// <inheritdoc cref="Path.GetTempFileName"/>
+        string GetTempFileName();
+        /// <inheritdoc cref="Path.GetTempPath"/>
+        string GetTempPath();
+        /// <inheritdoc cref="Path.HasExtension"/>
+        bool HasExtension(string path);
+        /// <inheritdoc cref="Path.IsPathRooted"/>
+        bool IsPathRooted(string path);
+    }
+}
\ No newline at end of file
diff --git a/System.IO.Abstractions/PathBase.cs b/System.IO.Abstractions/PathBase.cs
index 87b8b687e..18a523728 100644
--- a/System.IO.Abstractions/PathBase.cs
+++ b/System.IO.Abstractions/PathBase.cs
@@ -2,7 +2,7 @@
 {
     /// <inheritdoc cref="Path"/>
     [Serializable]
-    public abstract class PathBase
+    public abstract class PathBase : IPath
     {
         protected PathBase(IFileSystem fileSystem)
         {
diff --git a/version.json b/version.json
index 785fbb59a..63af7b263 100644
--- a/version.json
+++ b/version.json
@@ -1,6 +1,6 @@
 {
     "$schema": "https://raw.githubusercontent.com/AArnott/Nerdbank.GitVersioning/master/src/NerdBank.GitVersioning/version.schema.json",
-    "version": "3.1",
+    "version": "4.0",
     "assemblyVersion": {
       "precision": "major"
     },