diff --git a/core/module.rbs b/core/module.rbs
new file mode 100644
index 0000000..d5bc92f
--- /dev/null
+++ b/core/module.rbs
@@ -0,0 +1,2 @@
+class Module < Object
+end
diff --git a/core/object.rbs b/core/object.rbs
index f0a8776..b41c297 100644
--- a/core/object.rbs
+++ b/core/object.rbs
@@ -30,9 +30,8 @@ class Object < BasicObject
 
   def block_given?: () -> bool
 
-  # TODO: Module
-  def kind_of?: (Class) -> bool
-  def self.kind_of?: (Class) -> bool
+  def kind_of?: (Class | Module) -> bool
+  def self.kind_of?: (Class | Module) -> bool
 
   alias is_a? kind_of?
   alias self.is_a? self.kind_of?
@@ -62,12 +61,11 @@ class Object < BasicObject
   # TODO: Symbol
   # def self.attr_accessor: (*Symbol names) -> void
 
-  # TODO: Module
-  # def include: (*Module mods) -> void
-  # def self.include: (*Module mods) -> void
-  #
-  # alias extend include
-  # alias self.extend include
+  def include: (Module, *Module mods) -> void
+  def self.include: (Module, *Module mods) -> void
+
+  alias extend include
+  alias self.extend self.include
 
   # TODO: Array, Symbol
   # def self.constants: (?bool inherit) -> Array[Symbol]
diff --git a/test/module.rb b/test/module.rb
new file mode 100644
index 0000000..0f4f360
--- /dev/null
+++ b/test/module.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+# @type const Mod: Mod
+module Mod
+  # @type method method: () -> void
+  def self.method
+    puts
+  end
+end
diff --git a/test/object.rb b/test/object.rb
index 2a828a3..7914663 100644
--- a/test/object.rb
+++ b/test/object.rb
@@ -7,6 +7,11 @@
 # rubocop:disable Style/ClassCheck
 # rubocop:disable Style/FormatString
 # rubocop:disable Style/RedundantFormat
+# rubocop:disable Style/MixinGrouping
+# rubocop:disable Layout/EmptyLinesAroundAccessModifier
+
+# @type const TestMod: Module
+module TestMod end
 
 object = Object.new
 
@@ -43,10 +48,14 @@
 object.block_given?
 
 object.kind_of? Object
+object.kind_of? TestMod
 Object.kind_of? Object
+Object.kind_of? TestMod
 
 object.is_a? Object
+object.is_a? TestMod
 Object.is_a? Object
+Object.is_a? TestMod
 
 object.nil?
 Object.nil?
@@ -71,8 +80,17 @@
 object.raise
 object.raise 'error'
 
-# @type const A: A
+# @type const A: Class
 class A
+  # @type const TestMod: Module
+  module TestMod end
+
+  include TestMod
+  include TestMod, TestMod, TestMod
+
+  extend TestMod
+  extend TestMod, TestMod, TestMod
+
   public
 
   private
@@ -80,6 +98,12 @@ class A
   protected
 end
 
+Object.include TestMod
+Object.include TestMod, TestMod, TestMod
+
+Object.extend TestMod
+Object.extend TestMod, TestMod, TestMod
+
 sprintf "%d\n", 123
 
 printf "%d\n", 123