diff --git a/include/natalie/string_object.hpp b/include/natalie/string_object.hpp
index 2733211231..9e3028b89c 100644
--- a/include/natalie/string_object.hpp
+++ b/include/natalie/string_object.hpp
@@ -152,6 +152,7 @@ class StringObject : public Object {
     bool eq(Env *, Value arg);
     Value eqtilde(Env *, Value);
     Value force_encoding(Env *, Value);
+    bool include(Env *, Value);
     Value ljust(Env *, Value, Value);
     Value lstrip(Env *) const;
     Value lstrip_in_place(Env *);
diff --git a/lib/natalie/compiler/binding_gen.rb b/lib/natalie/compiler/binding_gen.rb
index e37bf146d6..c788c6ace9 100644
--- a/lib/natalie/compiler/binding_gen.rb
+++ b/lib/natalie/compiler/binding_gen.rb
@@ -796,6 +796,7 @@ def generate_name
 gen.binding('String', 'eql?', 'StringObject', 'eql', argc: 1, pass_env: false, pass_block: false, return_type: :bool)
 gen.binding('String', 'force_encoding', 'StringObject', 'force_encoding', argc: 1, pass_env: true, pass_block: false, return_type: :Object)
 gen.binding('String', 'gsub', 'StringObject', 'gsub', argc: 1..2, pass_env: true, pass_block: true, return_type: :Object)
+gen.binding('String', 'include?', 'StringObject', 'include', argc: 1, pass_env: true, pass_block: false, return_type: :bool)
 gen.binding('String', 'index', 'StringObject', 'index', argc: 1, pass_env: true, pass_block: false, return_type: :Object)
 gen.binding('String', 'initialize', 'StringObject', 'initialize', argc: 0..1, pass_env: true, pass_block: false, return_type: :Object)
 gen.binding('String', 'inspect', 'StringObject', 'inspect', argc: 0, pass_env: true, pass_block: false, return_type: :Object)
diff --git a/spec/core/string/include_spec.rb b/spec/core/string/include_spec.rb
new file mode 100644
index 0000000000..407c810804
--- /dev/null
+++ b/spec/core/string/include_spec.rb
@@ -0,0 +1,36 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+describe "String#include? with String" do
+  it "returns true if self contains other_str" do
+    "hello".include?("lo").should == true
+    "hello".include?("ol").should == false
+  end
+
+  it "ignores subclass differences" do
+    "hello".include?(StringSpecs::MyString.new("lo")).should == true
+    StringSpecs::MyString.new("hello").include?("lo").should == true
+    StringSpecs::MyString.new("hello").include?(StringSpecs::MyString.new("lo")).should == true
+  end
+
+  it "tries to convert other to string using to_str" do
+    other = mock('lo')
+    other.should_receive(:to_str).and_return("lo")
+
+    "hello".include?(other).should == true
+  end
+
+  it "raises a TypeError if other can't be converted to string" do
+    -> { "hello".include?([])       }.should raise_error(TypeError)
+    -> { "hello".include?('h'.ord)  }.should raise_error(TypeError)
+    -> { "hello".include?(mock('x')) }.should raise_error(TypeError)
+  end
+
+  # NATFIXME: Implement EUC-JP encoding
+  xit "raises an Encoding::CompatibilityError if the encodings are incompatible" do
+    pat = "ア".encode Encoding::EUC_JP
+    -> do
+      "あれ".include?(pat)
+    end.should raise_error(Encoding::CompatibilityError)
+  end
+end
diff --git a/src/string_object.cpp b/src/string_object.cpp
index 7534c2bbdd..85d38408a2 100644
--- a/src/string_object.cpp
+++ b/src/string_object.cpp
@@ -657,6 +657,14 @@ Value StringObject::split(Env *env, Value splitter, Value max_count_value) {
     }
 }
 
+bool StringObject::include(Env *env, Value arg) {
+    auto to_str = "to_str"_s;
+    if (!arg->is_string() && arg->respond_to(env, to_str))
+        arg = arg->send(env, to_str);
+    arg->assert_type(env, Object::Type::String, "String");
+    return ::strstr(c_str(), arg->as_string()->c_str()) != nullptr;
+}
+
 Value StringObject::ljust(Env *env, Value length_obj, Value pad_obj) {
     length_obj->assert_type(env, Object::Type::Integer, "Integer");
     size_t length = length_obj->as_integer()->to_nat_int_t() < 0 ? 0 : length_obj->as_integer()->to_nat_int_t();