diff --git a/Gemfile b/Gemfile
index 7ddc41d1b..5b8b7cc6b 100644
--- a/Gemfile
+++ b/Gemfile
@@ -16,6 +16,7 @@ gem 'stackprof'
 gem "goodcheck"
 gem "dbm"
 gem 'digest'
+gem 'tempfile'
 
 # Test gems
 gem "rbs-amber", path: "test/assets/test-gem"
diff --git a/stdlib/tempfile/0/tempfile.rbs b/stdlib/tempfile/0/tempfile.rbs
new file mode 100644
index 000000000..e7e164ca6
--- /dev/null
+++ b/stdlib/tempfile/0/tempfile.rbs
@@ -0,0 +1,267 @@
+# A utility class for managing temporary files. When you create a Tempfile
+# object, it will create a temporary file with a unique filename. A Tempfile
+# objects behaves just like a File object, and you can perform all the usual
+# file operations on it: reading data, writing data, changing its permissions,
+# etc. So although this class does not explicitly document all instance methods
+# supported by File, you can in fact call any File instance method on a Tempfile
+# object.
+#
+# ## Synopsis
+#
+#     require 'tempfile'
+#
+#     file = Tempfile.new('foo')
+#     file.path      # => A unique filename in the OS's temp directory,
+#                    #    e.g.: "/tmp/foo.24722.0"
+#                    #    This filename contains 'foo' in its basename.
+#     file.write("hello world")
+#     file.rewind
+#     file.read      # => "hello world"
+#     file.close
+#     file.unlink    # deletes the temp file
+#
+# ## Good practices
+#
+# ### Explicit close
+#
+# When a Tempfile object is garbage collected, or when the Ruby interpreter
+# exits, its associated temporary file is automatically deleted. This means
+# that's it's unnecessary to explicitly delete a Tempfile after use, though it's
+# good practice to do so: not explicitly deleting unused Tempfiles can
+# potentially leave behind large amounts of tempfiles on the filesystem until
+# they're garbage collected. The existence of these temp files can make it
+# harder to determine a new Tempfile filename.
+#
+# Therefore, one should always call #unlink or close in an ensure block, like
+# this:
+#
+#     file = Tempfile.new('foo')
+#     begin
+#        # ...do something with file...
+#     ensure
+#        file.close
+#        file.unlink   # deletes the temp file
+#     end
+#
+# Tempfile.create { ... } exists for this purpose and is more convenient to use.
+# Note that Tempfile.create returns a File instance instead of a Tempfile, which
+# also avoids the overhead and complications of delegation.
+#
+#     Tempfile.open('foo') do |file|
+#        # ...do something with file...
+#     end
+#
+# ### Unlink after creation
+#
+# On POSIX systems, it's possible to unlink a file right after creating it, and
+# before closing it. This removes the filesystem entry without closing the file
+# handle, so it ensures that only the processes that already had the file handle
+# open can access the file's contents. It's strongly recommended that you do
+# this if you do not want any other processes to be able to read from or write
+# to the Tempfile, and you do not need to know the Tempfile's filename either.
+#
+# For example, a practical use case for unlink-after-creation would be this: you
+# need a large byte buffer that's too large to comfortably fit in RAM, e.g. when
+# you're writing a web server and you want to buffer the client's file upload
+# data.
+#
+# Please refer to #unlink for more information and a code example.
+#
+# ## Minor notes
+#
+# Tempfile's filename picking method is both thread-safe and inter-process-safe:
+# it guarantees that no other threads or processes will pick the same filename.
+#
+# Tempfile itself however may not be entirely thread-safe. If you access the
+# same Tempfile object from multiple threads then you should protect it with a
+# mutex.
+class Tempfile < File
+  # Creates a temporary file as a usual File object (not a Tempfile). It does not
+  # use finalizer and delegation, which makes it more efficient and reliable.
+  #
+  # If no block is given, this is similar to Tempfile.new except creating File
+  # instead of Tempfile. In that case, the created file is not removed
+  # automatically. You should use File.unlink to remove it.
+  #
+  # If a block is given, then a File object will be constructed, and the block is
+  # invoked with the object as the argument. The File object will be automatically
+  # closed and the temporary file is removed after the block terminates, releasing
+  # all resources that the block created. The call returns the value of the block.
+  #
+  # In any case, all arguments (`basename`, `tmpdir`, `mode`, and `**options`)
+  # will be treated the same as for Tempfile.new.
+  #
+  #     Tempfile.create('foo', '/home/temp') do |f|
+  #        # ... do something with f ...
+  #     end
+  #
+  def self.create: (?String basename, ?String? tmpdir, ?mode: Integer, **untyped) -> File
+
+  # Creates a new Tempfile.
+  #
+  # This method is not recommended and exists mostly for backward compatibility.
+  # Please use Tempfile.create instead, which avoids the cost of delegation, does
+  # not rely on a finalizer, and also unlinks the file when given a block.
+  #
+  # Tempfile.open is still appropriate if you need the Tempfile to be unlinked by
+  # a finalizer and you cannot explicitly know where in the program the Tempfile
+  # can be unlinked safely.
+  #
+  # If no block is given, this is a synonym for Tempfile.new.
+  #
+  # If a block is given, then a Tempfile object will be constructed, and the block
+  # is run with the Tempfile object as argument. The Tempfile object will be
+  # automatically closed after the block terminates. However, the file will
+  # **not** be unlinked and needs to be manually unlinked with Tempfile#close! or
+  # Tempfile#unlink. The finalizer will try to unlink but should not be relied
+  # upon as it can keep the file on the disk much longer than intended. For
+  # instance, on CRuby, finalizers can be delayed due to conservative stack
+  # scanning and references left in unused memory.
+  #
+  # The call returns the value of the block.
+  #
+  # In any case, all arguments (`*args`) will be passed to Tempfile.new.
+  #
+  #     Tempfile.open('foo', '/home/temp') do |f|
+  #        # ... do something with f ...
+  #     end
+  #
+  #     # Equivalent:
+  #     f = Tempfile.open('foo', '/home/temp')
+  #     begin
+  #        # ... do something with f ...
+  #     ensure
+  #        f.close
+  #     end
+  #
+  def self.open: (*untyped args, **untyped) -> Tempfile
+
+  public
+
+  # Closes the file. If `unlink_now` is true, then the file will be unlinked
+  # (deleted) after closing. Of course, you can choose to later call #unlink if
+  # you do not unlink it now.
+  #
+  # If you don't explicitly unlink the temporary file, the removal will be delayed
+  # until the object is finalized.
+  #
+  def close: (?boolish unlink_now) -> void
+
+  # Closes and unlinks (deletes) the file. Has the same effect as called
+  # `close(true)`.
+  #
+  def close!: () -> void
+
+  alias delete unlink
+
+  def inspect: () -> String
+
+  alias length size
+
+  # Opens or reopens the file with mode "r+".
+  #
+  def open: () -> File
+
+  # Returns the full path name of the temporary file. This will be nil if #unlink
+  # has been called.
+  #
+  def path: () -> String?
+
+  # Returns the size of the temporary file.  As a side effect, the IO buffer is
+  # flushed before determining the size.
+  #
+  def size: () -> Integer
+
+  # Unlinks (deletes) the file from the filesystem. One should always unlink the
+  # file after using it, as is explained in the "Explicit close" good practice
+  # section in the Tempfile overview:
+  #
+  #     file = Tempfile.new('foo')
+  #     begin
+  #        # ...do something with file...
+  #     ensure
+  #        file.close
+  #        file.unlink   # deletes the temp file
+  #     end
+  #
+  # ### Unlink-before-close
+  #
+  # On POSIX systems it's possible to unlink a file before closing it. This
+  # practice is explained in detail in the Tempfile overview (section "Unlink
+  # after creation"); please refer there for more information.
+  #
+  # However, unlink-before-close may not be supported on non-POSIX operating
+  # systems. Microsoft Windows is the most notable case: unlinking a non-closed
+  # file will result in an error, which this method will silently ignore. If you
+  # want to practice unlink-before-close whenever possible, then you should write
+  # code like this:
+  #
+  #     file = Tempfile.new('foo')
+  #     file.unlink   # On Windows this silently fails.
+  #     begin
+  #        # ... do something with file ...
+  #     ensure
+  #        file.close!   # Closes the file handle. If the file wasn't unlinked
+  #                      # because #unlink failed, then this method will attempt
+  #                      # to do so again.
+  #     end
+  #
+  def unlink: () -> void
+
+  class Remover
+    public
+
+    def call: (*untyped args) -> void
+
+    private
+
+    def initialize: (::Tempfile tmpfile) -> void
+  end
+
+  private
+
+  # Creates a temporary file with permissions 0600 (= only readable and writable
+  # by the owner) and opens it with mode "w+".
+  #
+  # It is recommended to use Tempfile.create { ... } instead when possible,
+  # because that method avoids the cost of delegation and does not rely on a
+  # finalizer to close and unlink the file, which is unreliable.
+  #
+  # The `basename` parameter is used to determine the name of the temporary file.
+  # You can either pass a String or an Array with 2 String elements. In the former
+  # form, the temporary file's base name will begin with the given string. In the
+  # latter form, the temporary file's base name will begin with the array's first
+  # element, and end with the second element. For example:
+  #
+  #     file = Tempfile.new('hello')
+  #     file.path  # => something like: "/tmp/hello2843-8392-92849382--0"
+  #
+  #     # Use the Array form to enforce an extension in the filename:
+  #     file = Tempfile.new(['hello', '.jpg'])
+  #     file.path  # => something like: "/tmp/hello2843-8392-92849382--0.jpg"
+  #
+  # The temporary file will be placed in the directory as specified by the
+  # `tmpdir` parameter. By default, this is `Dir.tmpdir`.
+  #
+  #     file = Tempfile.new('hello', '/home/aisaka')
+  #     file.path  # => something like: "/home/aisaka/hello2843-8392-92849382--0"
+  #
+  # You can also pass an options hash. Under the hood, Tempfile creates the
+  # temporary file using `File.open`. These options will be passed to `File.open`.
+  # This is mostly useful for specifying encoding options, e.g.:
+  #
+  #     Tempfile.new('hello', '/home/aisaka', encoding: 'ascii-8bit')
+  #
+  #     # You can also omit the 'tmpdir' parameter:
+  #     Tempfile.new('hello', encoding: 'ascii-8bit')
+  #
+  # Note: `mode` keyword argument, as accepted by Tempfile, can only be numeric,
+  # combination of the modes defined in File::Constants.
+  #
+  # ### Exceptions
+  #
+  # If Tempfile.new cannot find a unique filename within a limited number of
+  # tries, then it will raise an exception.
+  #
+  def initialize: (?String basename, ?String? tmpdir, ?mode: Integer, **untyped) -> void
+end
diff --git a/test/stdlib/tempfile/TempfileRemover_test.rb b/test/stdlib/tempfile/TempfileRemover_test.rb
new file mode 100644
index 000000000..24f5033b2
--- /dev/null
+++ b/test/stdlib/tempfile/TempfileRemover_test.rb
@@ -0,0 +1,27 @@
+require_relative "../test_helper"
+require 'tempfile'
+
+class TempfileRemoverSingletonTest < Test::Unit::TestCase
+  include TypeAssertions
+
+  library "tempfile"
+  testing "singleton(::Tempfile::Remover)"
+
+  def test_initialize
+    assert_send_type "(::Tempfile tmpfile) -> void",
+                     Tempfile::Remover, :new, Tempfile.new('README.md')
+  end
+end
+
+class TempfileRemoverTest < Test::Unit::TestCase
+  include TypeAssertions
+
+  library "tempfile"
+  testing "::Tempfile::Remover"
+
+  def test_call
+    assert_send_type "(*untyped args) -> void",
+                     Tempfile::Remover.new(Tempfile.new('README.md')),
+                     :call
+  end
+end
diff --git a/test/stdlib/tempfile/Tempfile_test.rb b/test/stdlib/tempfile/Tempfile_test.rb
new file mode 100644
index 000000000..45b1c60a5
--- /dev/null
+++ b/test/stdlib/tempfile/Tempfile_test.rb
@@ -0,0 +1,101 @@
+require_relative "../test_helper"
+require 'tempfile'
+
+class TempfileSingletonTest < Test::Unit::TestCase
+  include TypeAssertions
+
+  library "tempfile"
+  testing "singleton(::Tempfile)"
+
+
+  def test_open
+    assert_send_type "(*untyped args, **untyped) -> ::Tempfile",
+                     Tempfile, :open, 'README.md'
+  end
+
+  def test_new
+    assert_send_type "(?::String basename, ?::String? tmpdir, ?mode: ::Integer, **untyped) -> ::Tempfile",
+                     Tempfile, :new, 'README.md', '/tmp', mode: 0
+  end
+
+  def test_create
+    assert_send_type "(?::String basename, ?::String? tmpdir, ?mode: ::Integer, **untyped) -> ::File",
+                     Tempfile, :create, 'README.md', '/tmp', mode: 0
+  end
+
+  def test_initialize
+    assert_send_type "(?::String basename, ?::String? tmpdir, ?mode: ::Integer, **untyped) -> void",
+                     Tempfile, :new, 'README.md', '/tmp', mode: 0
+  end
+end
+
+class TempfileTest < Test::Unit::TestCase
+  include TypeAssertions
+
+  library "tempfile"
+  testing "::Tempfile"
+
+
+  def test_open
+    assert_send_type "() -> ::File",
+                     Tempfile.new('README.md'), :open
+  end
+
+  def test_inspect
+    assert_send_type "() -> ::String",
+                     Tempfile.new('README.md'), :inspect
+  end
+
+  def test_close
+    assert_send_type "() -> void",
+                     Tempfile.new('README.md'), :close
+
+    assert_send_type "(true) -> void",
+                     Tempfile.new('README.md'), :close, true
+
+    assert_send_type "(String) -> void",
+                     Tempfile.new('README.md'), :close, "true"
+
+    assert_send_type "(false) -> void",
+                     Tempfile.new('README.md'), :close, false
+  end
+
+  def test_path
+    assert_send_type "() -> ::String?",
+                     Tempfile.new('README.md'), :path
+
+    assert_send_type "() -> ::String?",
+                     Tempfile.new('README.md').tap(&:unlink), :path
+  end
+
+  def test_size
+    assert_send_type "() -> ::Integer",
+                     Tempfile.new('README.md'), :size
+  end
+
+  def test_close!
+    assert_send_type "() -> void",
+                     Tempfile.new, :close!
+  end
+
+  def test_unlink
+    assert_send_type "() -> void",
+                     Tempfile.new, :unlink
+
+    assert_send_type "() -> void",
+                     Tempfile.new('README.md').tap(&:unlink), :unlink
+  end
+
+  def test_delete
+    assert_send_type "() -> bool?",
+                     Tempfile.new, :delete
+
+    assert_send_type  "() -> bool?",
+                     Tempfile.new('README.md').tap(&:unlink), :delete
+  end
+
+  def test_length
+    assert_send_type "() -> ::Integer",
+                     Tempfile.new('README.md'), :length
+  end
+end