diff --git a/src/CommandLineUtils/Attributes/OptionAttribute.cs b/src/CommandLineUtils/Attributes/OptionAttribute.cs
index 36fd21f8..6f7e1ac9 100755
--- a/src/CommandLineUtils/Attributes/OptionAttribute.cs
+++ b/src/CommandLineUtils/Attributes/OptionAttribute.cs
@@ -90,7 +90,7 @@ internal CommandOption Configure(CommandLineApplication app, PropertyInfo prop)
 
             option.Description ??= prop.Name;
 
-            app.Options.Add(option);
+            app.AddOption(option);
             return option;
         }
 
diff --git a/src/CommandLineUtils/CommandLineApplication.cs b/src/CommandLineUtils/CommandLineApplication.cs
index 85a0fc36..fa2cfe76 100644
--- a/src/CommandLineUtils/CommandLineApplication.cs
+++ b/src/CommandLineUtils/CommandLineApplication.cs
@@ -56,6 +56,10 @@ static CommandLineApplication()
         private readonly Lazy<IServiceProvider> _services;
         private readonly ConventionContext _conventionContext;
         private readonly List<IConvention> _conventions = new List<IConvention>();
+        private readonly List<CommandArgument> _arguments = new List<CommandArgument>();
+        private readonly List<CommandOption> _options = new List<CommandOption>();
+        private readonly List<CommandLineApplication> _subcommands = new List<CommandLineApplication>();
+        internal readonly List<string> _remainingArguments = new List<string>();
 
         /// <summary>
         /// Initializes a new instance of <see cref="CommandLineApplication"/>.
@@ -109,10 +113,6 @@ internal CommandLineApplication(
         {
             _context = context ?? throw new ArgumentNullException(nameof(context));
             Parent = parent;
-            Options = new List<CommandOption>();
-            Arguments = new List<CommandArgument>();
-            Commands = new List<CommandLineApplication>();
-            RemainingArguments = new List<string>();
             _helpTextGenerator = helpTextGenerator ?? throw new ArgumentNullException(nameof(helpTextGenerator));
             _handler = DefaultAction;
             _validationErrorHandler = DefaultValidationErrorHandler;
@@ -186,7 +186,7 @@ public string? Name
         /// <summary>
         /// Available command-line options on this command. Use <see cref="GetOptions"/> to get all available options, which may include inherited options.
         /// </summary>
-        public List<CommandOption> Options { get; private set; }
+        public IReadOnlyCollection<CommandOption> Options => _options;
 
         /// <summary>
         /// Whether a Pager should be used to display help text.
@@ -239,13 +239,13 @@ public CommandOption? OptionHelp
         /// <summary>
         /// Required command-line arguments.
         /// </summary>
-        public List<CommandArgument> Arguments { get; private set; }
+        public IReadOnlyList<CommandArgument> Arguments => _arguments;
 
         /// <summary>
         /// When initialized when <see cref="UnrecognizedArgumentHandling"/> is <see cref="McMaster.Extensions.CommandLineUtils.UnrecognizedArgumentHandling.StopParsingAndCollect" />,
         /// this will contain any unrecognized arguments.
         /// </summary>
-        public List<string> RemainingArguments { get; private set; }
+        public IReadOnlyList<string> RemainingArguments => _remainingArguments;
 
         /// <summary>
         /// Configures what the parser should do when it runs into an unexpected argument.
@@ -274,7 +274,7 @@ public UnrecognizedArgumentHandling UnrecognizedArgumentHandling
         /// <summary>
         /// Subcommands.
         /// </summary>
-        public List<CommandLineApplication> Commands { get; private set; }
+        public IReadOnlyCollection<CommandLineApplication> Commands => _subcommands;
 
         /// <summary>
         /// Determines if '--' can be used to separate known arguments and options from additional content passed to <see cref="RemainingArguments"/>.
@@ -454,7 +454,7 @@ public void AddSubcommand(CommandLineApplication subcommand)
 
             subcommand.Parent = this;
 
-            Commands.Add(subcommand);
+            _subcommands.Add(subcommand);
         }
 
         private void AssertCommandNameIsUnique(string? name, CommandLineApplication? commandToIgnore)
@@ -562,11 +562,20 @@ public CommandOption Option(string template, string description, CommandOptionTy
                 Description = description,
                 Inherited = inherited
             };
-            Options.Add(option);
+            AddOption(option);
             configuration(option);
             return option;
         }
 
+        /// <summary>
+        /// Add an option to the definition of this command
+        /// </summary>
+        /// <param name="option"></param>
+        public void AddOption(CommandOption option)
+        {
+            _options.Add(option);
+        }
+
         /// <summary>
         /// Adds a command line option with values that should be parsable into <typeparamref name="T" />.
         /// </summary>
@@ -591,7 +600,7 @@ public CommandOption<T> Option<T>(string template, string description, CommandOp
                 Description = description,
                 Inherited = inherited
             };
-            Options.Add(option);
+            AddOption(option);
             configuration(option);
             return option;
         }
@@ -662,14 +671,18 @@ public CommandArgument<T> Argument<T>(string name, string description, Action<Co
             return argument;
         }
 
-        private void AddArgument(CommandArgument argument)
+        /// <summary>
+        /// Add an argument to the definition of this command.
+        /// </summary>
+        /// <param name="argument"></param>
+        public void AddArgument(CommandArgument argument)
         {
             var lastArg = Arguments.LastOrDefault();
             if (lastArg != null && lastArg.MultipleValues)
             {
                 throw new InvalidOperationException(Strings.OnlyLastArgumentCanAllowMultipleValues(lastArg.Name));
             }
-            Arguments.Add(argument);
+            _arguments.Add(argument);
         }
 
         /// <summary>
@@ -708,7 +721,7 @@ private void Reset()
             }
 
             IsShowingInformation = default;
-            RemainingArguments.Clear();
+            _remainingArguments.Clear();
         }
 
         /// <summary>
diff --git a/src/CommandLineUtils/Conventions/ArgumentAttributeConvention.cs b/src/CommandLineUtils/Conventions/ArgumentAttributeConvention.cs
index 132e2455..860e67d1 100644
--- a/src/CommandLineUtils/Conventions/ArgumentAttributeConvention.cs
+++ b/src/CommandLineUtils/Conventions/ArgumentAttributeConvention.cs
@@ -64,7 +64,7 @@ public virtual void Apply(ConventionContext context)
                     }
                 }
 
-                context.Application.Arguments.Add(arg.Value);
+                context.Application.AddArgument(arg.Value);
             }
         }
 
diff --git a/src/CommandLineUtils/Conventions/DefaultHelpOptionConvention.cs b/src/CommandLineUtils/Conventions/DefaultHelpOptionConvention.cs
index bcadccc3..34a53ba9 100644
--- a/src/CommandLineUtils/Conventions/DefaultHelpOptionConvention.cs
+++ b/src/CommandLineUtils/Conventions/DefaultHelpOptionConvention.cs
@@ -70,7 +70,7 @@ public void Apply(ConventionContext context)
             if (help.LongName != null || help.ShortName != null || help.SymbolName != null)
             {
                 context.Application.OptionHelp = help;
-                context.Application.Options.Add(help);
+                context.Application.AddOption(help);
             }
         }
     }
diff --git a/src/CommandLineUtils/Conventions/RemainingArgsPropertyConvention.cs b/src/CommandLineUtils/Conventions/RemainingArgsPropertyConvention.cs
index fdf1ec2e..94940ce7 100644
--- a/src/CommandLineUtils/Conventions/RemainingArgsPropertyConvention.cs
+++ b/src/CommandLineUtils/Conventions/RemainingArgsPropertyConvention.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Reflection;
 
 namespace McMaster.Extensions.CommandLineUtils.Conventions
diff --git a/src/CommandLineUtils/Internal/CommandLineProcessor.cs b/src/CommandLineUtils/Internal/CommandLineProcessor.cs
index 120803af..116fb701 100644
--- a/src/CommandLineUtils/Internal/CommandLineProcessor.cs
+++ b/src/CommandLineUtils/Internal/CommandLineProcessor.cs
@@ -335,7 +335,7 @@ private bool ProcessUnexpectedArg(string argTypeName, string? argValue = null)
 
                 case UnrecognizedArgumentHandling.CollectAndContinue:
                     var arg = _enumerator.Current;
-                    _currentCommand.RemainingArguments.Add(arg.Raw);
+                    _currentCommand._remainingArguments.Add(arg.Raw);
                     return true;
 
                 case UnrecognizedArgumentHandling.StopParsingAndCollect:
@@ -354,7 +354,7 @@ private void AddRemainingArgumentValues()
                 var arg = _enumerator.Current;
                 if (arg != null)
                 {
-                    _currentCommand.RemainingArguments.Add(arg.Raw);
+                    _currentCommand._remainingArguments.Add(arg.Raw);
                 }
             } while (_enumerator.MoveNext());
         }
diff --git a/src/CommandLineUtils/PublicAPI.Shipped.txt b/src/CommandLineUtils/PublicAPI.Shipped.txt
index 7ceb21b6..1476d1c4 100644
--- a/src/CommandLineUtils/PublicAPI.Shipped.txt
+++ b/src/CommandLineUtils/PublicAPI.Shipped.txt
@@ -105,7 +105,7 @@ McMaster.Extensions.CommandLineUtils.CommandLineApplication.AllowArgumentSeparat
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Argument(string! name, string! description, bool multipleValues = false) -> McMaster.Extensions.CommandLineUtils.CommandArgument!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Argument(string! name, string! description, System.Action<McMaster.Extensions.CommandLineUtils.CommandArgument!>! configuration, bool multipleValues = false) -> McMaster.Extensions.CommandLineUtils.CommandArgument!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Argument<T>(string! name, string! description, System.Action<McMaster.Extensions.CommandLineUtils.CommandArgument<T>!>! configuration, bool multipleValues = false) -> McMaster.Extensions.CommandLineUtils.CommandArgument<T>!
-McMaster.Extensions.CommandLineUtils.CommandLineApplication.Arguments.get -> System.Collections.Generic.List<McMaster.Extensions.CommandLineUtils.CommandArgument!>!
+McMaster.Extensions.CommandLineUtils.CommandLineApplication.Arguments.get -> System.Collections.Generic.IReadOnlyList<McMaster.Extensions.CommandLineUtils.CommandArgument!>!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.ClusterOptions.get -> bool
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.ClusterOptions.set -> void
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Command(string! name, System.Action<McMaster.Extensions.CommandLineUtils.CommandLineApplication!>! configuration) -> McMaster.Extensions.CommandLineUtils.CommandLineApplication!
@@ -114,7 +114,7 @@ McMaster.Extensions.CommandLineUtils.CommandLineApplication.CommandLineApplicati
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.CommandLineApplication(McMaster.Extensions.CommandLineUtils.HelpText.IHelpTextGenerator! helpTextGenerator, McMaster.Extensions.CommandLineUtils.IConsole! console, string! workingDirectory) -> void
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.CommandLineApplication(McMaster.Extensions.CommandLineUtils.IConsole! console, string! workingDirectory) -> void
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.CommandLineApplication(McMaster.Extensions.CommandLineUtils.IConsole! console) -> void
-McMaster.Extensions.CommandLineUtils.CommandLineApplication.Commands.get -> System.Collections.Generic.List<McMaster.Extensions.CommandLineUtils.CommandLineApplication!>!
+McMaster.Extensions.CommandLineUtils.CommandLineApplication.Commands.get -> System.Collections.Generic.IReadOnlyCollection<McMaster.Extensions.CommandLineUtils.CommandLineApplication!>!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Conventions.get -> McMaster.Extensions.CommandLineUtils.Conventions.IConventionBuilder!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Description.get -> string?
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Description.set -> void
@@ -152,7 +152,7 @@ McMaster.Extensions.CommandLineUtils.CommandLineApplication.Option<T>(string! te
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.OptionHelp.get -> McMaster.Extensions.CommandLineUtils.CommandOption?
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.OptionNameValueSeparators.get -> char[]!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.OptionNameValueSeparators.set -> void
-McMaster.Extensions.CommandLineUtils.CommandLineApplication.Options.get -> System.Collections.Generic.List<McMaster.Extensions.CommandLineUtils.CommandOption!>!
+McMaster.Extensions.CommandLineUtils.CommandLineApplication.Options.get -> System.Collections.Generic.IReadOnlyCollection<McMaster.Extensions.CommandLineUtils.CommandOption!>!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.OptionsComparison.get -> System.StringComparison
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.OptionsComparison.set -> void
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.OptionVersion.get -> McMaster.Extensions.CommandLineUtils.CommandOption?
@@ -161,7 +161,7 @@ McMaster.Extensions.CommandLineUtils.CommandLineApplication.Out.set -> void
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Parent.get -> McMaster.Extensions.CommandLineUtils.CommandLineApplication?
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Parent.set -> void
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.Parse(params string![]! args) -> McMaster.Extensions.CommandLineUtils.Abstractions.ParseResult!
-McMaster.Extensions.CommandLineUtils.CommandLineApplication.RemainingArguments.get -> System.Collections.Generic.List<string!>!
+McMaster.Extensions.CommandLineUtils.CommandLineApplication.RemainingArguments.get -> System.Collections.Generic.IReadOnlyList<string!>!
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.ResponseFileHandling.get -> McMaster.Extensions.CommandLineUtils.ResponseFileHandling
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.ResponseFileHandling.set -> void
 McMaster.Extensions.CommandLineUtils.CommandLineApplication.ShortVersionGetter.get -> System.Func<string?>?
diff --git a/src/CommandLineUtils/PublicAPI.Unshipped.txt b/src/CommandLineUtils/PublicAPI.Unshipped.txt
index c5893cb1..5018755e 100644
--- a/src/CommandLineUtils/PublicAPI.Unshipped.txt
+++ b/src/CommandLineUtils/PublicAPI.Unshipped.txt
@@ -3,3 +3,5 @@ McMaster.Extensions.CommandLineUtils.CommandArgument.HasValue.get -> bool
 McMaster.Extensions.CommandLineUtils.CommandArgument.TryParse(string? value) -> bool
 virtual McMaster.Extensions.CommandLineUtils.CommandArgument.Reset() -> void
 virtual McMaster.Extensions.CommandLineUtils.CommandOption.Reset() -> void
+McMaster.Extensions.CommandLineUtils.CommandLineApplication.AddArgument(McMaster.Extensions.CommandLineUtils.CommandArgument! argument) -> void
+McMaster.Extensions.CommandLineUtils.CommandLineApplication.AddOption(McMaster.Extensions.CommandLineUtils.CommandOption! option) -> void
diff --git a/test/CommandLineUtils.Tests/CommandLineApplicationTests.cs b/test/CommandLineUtils.Tests/CommandLineApplicationTests.cs
index 9e2fba19..daec85cb 100644
--- a/test/CommandLineUtils.Tests/CommandLineApplicationTests.cs
+++ b/test/CommandLineUtils.Tests/CommandLineApplicationTests.cs
@@ -745,7 +745,7 @@ public void OptionNameCanHaveSemicolon()
             {
                 LongName = "debug:hive"
             };
-            app.Options.Add(option);
+            app.AddOption(option);
             app.Parse("--debug:hive", "abc");
             Assert.Equal("abc", option.Value());
         }
@@ -759,7 +759,7 @@ public void OptionSeparatorMustNotUseSpace()
             {
                 LongName = "debug:hive"
             };
-            app.Options.Add(option);
+            app.AddOption(option);
 
             var ex = Assert.ThrowsAny<CommandParsingException>(() =>
                 app.Parse("--debug:hive", "abc"));
diff --git a/test/CommandLineUtils.Tests/HelpOptionAttributeTests.cs b/test/CommandLineUtils.Tests/HelpOptionAttributeTests.cs
index 08b032c6..e3a6f9d6 100644
--- a/test/CommandLineUtils.Tests/HelpOptionAttributeTests.cs
+++ b/test/CommandLineUtils.Tests/HelpOptionAttributeTests.cs
@@ -169,7 +169,10 @@ public void HelpOptionIsInherited()
             var outWriter = new StringWriter(sb);
             var app = new CommandLineApplication<Parent> { Out = outWriter };
             app.Conventions.UseDefaultConventions();
-            app.Commands.ForEach(f => f.Out = outWriter);
+            foreach (var subcmd in app.Commands)
+            {
+                subcmd.Out = outWriter;
+            }
             app.Execute("lvl2", "--help");
             var outData = sb.ToString();
 
@@ -210,7 +213,10 @@ public void NestedHelpOptionsChoosesHelpOptionNearestSelectedCommand(string[] ar
                 return 1;
             });
 
-            app.Commands.ForEach(f => f.Out = outWriter);
+            foreach (var subcmd in app.Commands)
+            {
+                subcmd.Out = outWriter;
+            }
 
             app.Execute(args);
             var outData = sb.ToString();
diff --git a/test/CommandLineUtils.Tests/OptionAttributeTests.cs b/test/CommandLineUtils.Tests/OptionAttributeTests.cs
index cb8de4c7..fd2878d9 100644
--- a/test/CommandLineUtils.Tests/OptionAttributeTests.cs
+++ b/test/CommandLineUtils.Tests/OptionAttributeTests.cs
@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
 using System.Reflection;
 using System.Reflection.Emit;
 using McMaster.Extensions.CommandLineUtils.Conventions;
@@ -314,7 +315,7 @@ private CommandOption CreateOption(Type propType, string propName)
             var appBuilder = typeof(CommandLineApplication<>).MakeGenericType(program);
             var app = (CommandLineApplication)Activator.CreateInstance(appBuilder, Util.EmptyArray<object>());
             app.Conventions.UseOptionAttributes();
-            return app.Options[0];
+            return app.Options.First();
         }
     }
 }
diff --git a/test/CommandLineUtils.Tests/ValueParserProviderCustomTests.cs b/test/CommandLineUtils.Tests/ValueParserProviderCustomTests.cs
index f4a14ebd..77edfb54 100644
--- a/test/CommandLineUtils.Tests/ValueParserProviderCustomTests.cs
+++ b/test/CommandLineUtils.Tests/ValueParserProviderCustomTests.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Globalization;
+using System.Linq;
 using System.Threading.Tasks;
 using McMaster.Extensions.CommandLineUtils.Abstractions;
 using Xunit;
@@ -227,7 +228,7 @@ public void CustomParsersAreAvailableToSubCommands()
 
             Assert.Equal(1, result);
             Assert.Equal(expectedDate, app.Model.MainDate);
-            Assert.Equal(expectedDate.AddSeconds(123456), ((CommandLineApplication<CustomParserProgramAttributesSubCommand>)app.Commands[0]).Model.SubDate);
+            Assert.Equal(expectedDate.AddSeconds(123456), app.Commands.OfType<CommandLineApplication<CustomParserProgramAttributesSubCommand>>().Single().Model.SubDate);
         }
 
         [Fact]
diff --git a/test/Hosting.CommandLine.Tests/HostBuilderExtensionsBuilderAPITests.cs b/test/Hosting.CommandLine.Tests/HostBuilderExtensionsBuilderAPITests.cs
index c3aa1d2d..84c395d5 100644
--- a/test/Hosting.CommandLine.Tests/HostBuilderExtensionsBuilderAPITests.cs
+++ b/test/Hosting.CommandLine.Tests/HostBuilderExtensionsBuilderAPITests.cs
@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using System.Threading.Tasks;
 using McMaster.Extensions.CommandLineUtils;
 using McMaster.Extensions.CommandLineUtils.Abstractions;