diff --git a/actionpack/lib/action_controller/metal.rb b/actionpack/lib/action_controller/metal.rb
index b9088e6d8617d..9ca0bbb9db0f6 100644
--- a/actionpack/lib/action_controller/metal.rb
+++ b/actionpack/lib/action_controller/metal.rb
@@ -148,7 +148,7 @@ def controller_name
     attr_internal :response, :request
     delegate :session, to: "@_request"
     delegate :headers, :status=, :location=, :content_type=,
-             :status, :location, :content_type, to: "@_response"
+             :status, :location, :content_type, :media_type, to: "@_response"
 
     def initialize
       @_request = nil
diff --git a/actionpack/lib/action_controller/metal/mime_responds.rb b/actionpack/lib/action_controller/metal/mime_responds.rb
index bf5e7a433f837..5c6f7fe396528 100644
--- a/actionpack/lib/action_controller/metal/mime_responds.rb
+++ b/actionpack/lib/action_controller/metal/mime_responds.rb
@@ -205,7 +205,7 @@ def respond_to(*mimes)
       yield collector if block_given?
 
       if format = collector.negotiate_format(request)
-        if content_type && content_type != format
+        if media_type && media_type != format
           raise ActionController::RespondToMismatchError
         end
         _process_format(format)
diff --git a/actionpack/lib/action_controller/metal/renderers.rb b/actionpack/lib/action_controller/metal/renderers.rb
index b81d3ef53946c..a251c29d2391e 100644
--- a/actionpack/lib/action_controller/metal/renderers.rb
+++ b/actionpack/lib/action_controller/metal/renderers.rb
@@ -157,7 +157,7 @@ def _render_to_body_with_renderer(options)
       json = json.to_json(options) unless json.kind_of?(String)
 
       if options[:callback].present?
-        if content_type.nil? || content_type == Mime[:json]
+        if media_type.nil? || media_type == Mime[:json]
           self.content_type = Mime[:js]
         end
 
diff --git a/actionpack/lib/action_controller/metal/rendering.rb b/actionpack/lib/action_controller/metal/rendering.rb
index 7d0a944381d8e..7f7c736965b39 100644
--- a/actionpack/lib/action_controller/metal/rendering.rb
+++ b/actionpack/lib/action_controller/metal/rendering.rb
@@ -73,7 +73,7 @@ def _set_html_content_type
       end
 
       def _set_rendered_content_type(format)
-        if format && !response.content_type
+        if format && !response.media_type
           self.content_type = format.to_s
         end
       end
diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index 69798f99e04be..5d137513d32cc 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -242,9 +242,8 @@ def content_type=(content_type)
       set_content_type new_header_info.mime_type, charset
     end
 
-    # Content type of response.
-    # It returns just MIME type and does NOT contain charset part.
-    def content_type
+    # Media type of response.
+    def media_type
       parsed_content_type_header.mime_type
     end
 
@@ -458,7 +457,7 @@ def munge_body_object(body)
     end
 
     def assign_default_content_type_and_charset!
-      return if content_type
+      return if media_type
 
       ct = parsed_content_type_header
       set_content_type(ct.mime_type || Mime[:html].to_s,
diff --git a/actionpack/lib/action_dispatch/testing/assertions.rb b/actionpack/lib/action_dispatch/testing/assertions.rb
index 08c2969685f48..dcaf914ac9335 100644
--- a/actionpack/lib/action_dispatch/testing/assertions.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions.rb
@@ -14,7 +14,7 @@ module Assertions
     include Rails::Dom::Testing::Assertions
 
     def html_document
-      @html_document ||= if @response.content_type.to_s.end_with?("xml")
+      @html_document ||= if @response.media_type.to_s.end_with?("xml")
         Nokogiri::XML::Document.parse(@response.body)
       else
         Nokogiri::HTML::Document.parse(@response.body)
diff --git a/actionpack/lib/action_dispatch/testing/test_response.rb b/actionpack/lib/action_dispatch/testing/test_response.rb
index 6f7c86fdcf6d6..f1dd4099c5f44 100644
--- a/actionpack/lib/action_dispatch/testing/test_response.rb
+++ b/actionpack/lib/action_dispatch/testing/test_response.rb
@@ -19,7 +19,7 @@ def parsed_body
     end
 
     def response_parser
-      @response_parser ||= RequestEncoder.parser(content_type)
+      @response_parser ||= RequestEncoder.parser(media_type)
     end
   end
 end
diff --git a/actionpack/test/controller/content_type_test.rb b/actionpack/test/controller/content_type_test.rb
index 636b025f2cc40..aeb0d071953a7 100644
--- a/actionpack/test/controller/content_type_test.rb
+++ b/actionpack/test/controller/content_type_test.rb
@@ -66,68 +66,68 @@ def setup
   def test_render_defaults
     get :render_defaults
     assert_equal "utf-8", @response.charset
-    assert_equal Mime[:text], @response.content_type
+    assert_equal Mime[:text], @response.media_type
   end
 
   def test_render_changed_charset_default
     with_default_charset "utf-16" do
       get :render_defaults
       assert_equal "utf-16", @response.charset
-      assert_equal Mime[:text], @response.content_type
+      assert_equal Mime[:text], @response.media_type
     end
   end
 
   # :ported:
   def test_content_type_from_body
     get :render_content_type_from_body
-    assert_equal Mime[:rss], @response.content_type
+    assert_equal Mime[:rss], @response.media_type
     assert_equal "utf-8", @response.charset
   end
 
   # :ported:
   def test_content_type_from_render
     get :render_content_type_from_render
-    assert_equal Mime[:rss], @response.content_type
+    assert_equal Mime[:rss], @response.media_type
     assert_equal "utf-8", @response.charset
   end
 
   # :ported:
   def test_charset_from_body
     get :render_charset_from_body
-    assert_equal Mime[:text], @response.content_type
+    assert_equal Mime[:text], @response.media_type
     assert_equal "utf-16", @response.charset
   end
 
   # :ported:
   def test_nil_charset_from_body
     get :render_nil_charset_from_body
-    assert_equal Mime[:text], @response.content_type
+    assert_equal Mime[:text], @response.media_type
     assert_equal "utf-8", @response.charset, @response.headers.inspect
   end
 
   def test_nil_default_for_erb
     with_default_charset nil do
       get :render_default_for_erb
-      assert_equal Mime[:html], @response.content_type
+      assert_equal Mime[:html], @response.media_type
       assert_nil @response.charset, @response.headers.inspect
     end
   end
 
   def test_default_for_erb
     get :render_default_for_erb
-    assert_equal Mime[:html], @response.content_type
+    assert_equal Mime[:html], @response.media_type
     assert_equal "utf-8", @response.charset
   end
 
   def test_default_for_builder
     get :render_default_for_builder
-    assert_equal Mime[:xml], @response.content_type
+    assert_equal Mime[:xml], @response.media_type
     assert_equal "utf-8", @response.charset
   end
 
   def test_change_for_builder
     get :render_change_for_builder
-    assert_equal Mime[:html], @response.content_type
+    assert_equal Mime[:html], @response.media_type
     assert_equal "utf-8", @response.charset
   end
 
@@ -148,22 +148,22 @@ class AcceptBasedContentTypeTest < ActionController::TestCase
   def test_render_default_content_types_for_respond_to
     @request.accept = Mime[:html].to_s
     get :render_default_content_types_for_respond_to
-    assert_equal Mime[:html], @response.content_type
+    assert_equal Mime[:html], @response.media_type
 
     @request.accept = Mime[:js].to_s
     get :render_default_content_types_for_respond_to
-    assert_equal Mime[:js], @response.content_type
+    assert_equal Mime[:js], @response.media_type
   end
 
   def test_render_default_content_types_for_respond_to_with_template
     @request.accept = Mime[:xml].to_s
     get :render_default_content_types_for_respond_to
-    assert_equal Mime[:xml], @response.content_type
+    assert_equal Mime[:xml], @response.media_type
   end
 
   def test_render_default_content_types_for_respond_to_with_overwrite
     @request.accept = Mime[:rss].to_s
     get :render_default_content_types_for_respond_to
-    assert_equal Mime[:xml], @response.content_type
+    assert_equal Mime[:xml], @response.media_type
   end
 end
diff --git a/actionpack/test/controller/integration_test.rb b/actionpack/test/controller/integration_test.rb
index 4dddd98f9f9a2..cce229b30d177 100644
--- a/actionpack/test/controller/integration_test.rb
+++ b/actionpack/test/controller/integration_test.rb
@@ -522,11 +522,11 @@ def test_accept_not_overridden_when_xhr_true
     with_test_route_set do
       get "/get", headers: { "Accept" => "application/json" }, xhr: true
       assert_equal "application/json", request.accept
-      assert_equal "application/json", response.content_type
+      assert_equal "application/json", response.media_type
 
       get "/get", headers: { "HTTP_ACCEPT" => "application/json" }, xhr: true
       assert_equal "application/json", request.accept
-      assert_equal "application/json", response.content_type
+      assert_equal "application/json", response.media_type
     end
   end
 
@@ -986,7 +986,7 @@ def test_standard_json_encoding_works
   def test_encoding_as_json
     post_to_foos as: :json do
       assert_response :success
-      assert_equal "application/json", request.content_type
+      assert_equal "application/json", request.media_type
       assert_equal "application/json", request.accepts.first.to_s
       assert_equal :json, request.format.ref
       assert_equal({ "foo" => "fighters" }, request.request_parameters)
@@ -1025,7 +1025,7 @@ def test_registering_custom_encoder
     post_to_foos as: :wibble do
       assert_response :success
       assert_equal "/foos_wibble", request.path
-      assert_equal "text/wibble", request.content_type
+      assert_equal "text/wibble", request.media_type
       assert_equal "text/wibble", request.accepts.first.to_s
       assert_equal :wibble, request.format.ref
       assert_equal Hash.new, request.request_parameters # Unregistered MIME Type can't be parsed.
diff --git a/actionpack/test/controller/localized_templates_test.rb b/actionpack/test/controller/localized_templates_test.rb
index d84a76fb46365..5c5cef66d56fe 100644
--- a/actionpack/test/controller/localized_templates_test.rb
+++ b/actionpack/test/controller/localized_templates_test.rb
@@ -43,6 +43,6 @@ def test_localized_template_has_correct_header_with_no_format_in_template_name
     I18n.locale = :it
     get :hello_world
     assert_equal "Ciao Mondo", @response.body
-    assert_equal "text/html",  @response.content_type
+    assert_equal "text/html",  @response.media_type
   end
 end
diff --git a/actionpack/test/controller/metal/renderers_test.rb b/actionpack/test/controller/metal/renderers_test.rb
index 5f0d1251285a7..f6558f13545ce 100644
--- a/actionpack/test/controller/metal/renderers_test.rb
+++ b/actionpack/test/controller/metal/renderers_test.rb
@@ -38,13 +38,13 @@ def test_render_json
     get :one
     assert_response :success
     assert_equal({ a: "b" }.to_json, @response.body)
-    assert_equal "application/json", @response.content_type
+    assert_equal "application/json", @response.media_type
   end
 
   def test_render_xml
     get :two
     assert_response :success
     assert_equal(" ", @response.body)
-    assert_equal "text/plain", @response.content_type
+    assert_equal "text/plain", @response.media_type
   end
 end
diff --git a/actionpack/test/controller/mime/respond_to_test.rb b/actionpack/test/controller/mime/respond_to_test.rb
index 2f8f19182880c..fc16c639fb455 100644
--- a/actionpack/test/controller/mime/respond_to_test.rb
+++ b/actionpack/test/controller/mime/respond_to_test.rb
@@ -423,12 +423,12 @@ def test_js_or_anything
   def test_using_defaults
     @request.accept = "*/*"
     get :using_defaults
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "Hello world!", @response.body
 
     @request.accept = "application/xml"
     get :using_defaults
-    assert_equal "application/xml", @response.content_type
+    assert_equal "application/xml", @response.media_type
     assert_equal "<p>Hello world!</p>\n", @response.body
   end
 
@@ -449,12 +449,12 @@ def test_using_defaults_with_all
   def test_using_defaults_with_type_list
     @request.accept = "*/*"
     get :using_defaults_with_type_list
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "Hello world!", @response.body
 
     @request.accept = "application/xml"
     get :using_defaults_with_type_list
-    assert_equal "application/xml", @response.content_type
+    assert_equal "application/xml", @response.media_type
     assert_equal "<p>Hello world!</p>\n", @response.body
   end
 
@@ -468,7 +468,7 @@ def test_using_conflicting_nested_js_then_html
   def test_using_non_conflicting_nested_js_then_js
     @request.accept = "*/*"
     get :using_non_conflicting_nested_js_then_js
-    assert_equal "text/javascript", @response.content_type
+    assert_equal "text/javascript", @response.media_type
     assert_equal "JS", @response.body
   end
 
@@ -499,12 +499,12 @@ def test_synonyms
   def test_custom_types
     @request.accept = "application/fancy-xml"
     get :custom_type_handling
-    assert_equal "application/fancy-xml", @response.content_type
+    assert_equal "application/fancy-xml", @response.media_type
     assert_equal "Fancy XML", @response.body
 
     @request.accept = "text/html"
     get :custom_type_handling
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "HTML", @response.body
   end
 
@@ -595,7 +595,7 @@ def test_json_with_callback_sets_javascript_content_type
     @request.accept = "application/json"
     get :json_with_callback
     assert_equal "/**/alert(JS)", @response.body
-    assert_equal "text/javascript", @response.content_type
+    assert_equal "text/javascript", @response.media_type
   end
 
   def test_xhr
@@ -605,13 +605,13 @@ def test_xhr
 
   def test_custom_constant
     get :custom_constant_handling, format: "mobile"
-    assert_equal "text/x-mobile", @response.content_type
+    assert_equal "text/x-mobile", @response.media_type
     assert_equal "Mobile", @response.body
   end
 
   def test_custom_constant_handling_without_block
     get :custom_constant_handling_without_block, format: "mobile"
-    assert_equal "text/x-mobile", @response.content_type
+    assert_equal "text/x-mobile", @response.media_type
     assert_equal "Mobile", @response.body
   end
 
@@ -664,7 +664,7 @@ def test_format_with_custom_response_type
     assert_equal '<html><div id="html">Hello future from Firefox!</div></html>', @response.body
 
     get :iphone_with_html_response_type, format: "iphone"
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal '<html><div id="iphone">Hello iPhone future from iPhone!</div></html>', @response.body
   end
 
@@ -672,7 +672,7 @@ def test_format_with_custom_response_type_and_request_headers
     @request.accept = "text/iphone"
     get :iphone_with_html_response_type
     assert_equal '<html><div id="iphone">Hello iPhone future from iPhone!</div></html>', @response.body
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_invalid_format
@@ -702,7 +702,7 @@ def test_variant_not_set_regular_unknown_format
 
   def test_variant_with_implicit_template_rendering
     get :variant_with_implicit_template_rendering, params: { v: :mobile }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "mobile", @response.body
   end
 
@@ -756,137 +756,137 @@ def test_variant_variant_not_set_and_without_implicit_rendering_from_xhr
 
   def test_variant_with_format_and_custom_render
     get :variant_with_format_and_custom_render, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "mobile", @response.body
   end
 
   def test_multiple_variants_for_format
     get :multiple_variants_for_format, params: { v: :tablet }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "tablet", @response.body
   end
 
   def test_no_variant_in_variant_setup
     get :variant_plus_none_for_format
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "none", @response.body
   end
 
   def test_variant_inline_syntax
     get :variant_inline_syntax
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "none", @response.body
 
     get :variant_inline_syntax, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
   end
 
   def test_variant_inline_syntax_with_format
     get :variant_inline_syntax, format: :js
-    assert_equal "text/javascript", @response.content_type
+    assert_equal "text/javascript", @response.media_type
     assert_equal "js", @response.body
   end
 
   def test_variant_inline_syntax_without_block
     get :variant_inline_syntax_without_block, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
   end
 
   def test_variant_any
     get :variant_any, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
 
     get :variant_any, params: { v: :tablet }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "any", @response.body
 
     get :variant_any, params: { v: :phablet }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "any", @response.body
   end
 
   def test_variant_any_any
     get :variant_any_any
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "any", @response.body
 
     get :variant_any_any, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
 
     get :variant_any_any, params: { v: :yolo }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "any", @response.body
   end
 
   def test_variant_inline_any
     get :variant_any, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
 
     get :variant_inline_any, params: { v: :tablet }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "any", @response.body
 
     get :variant_inline_any, params: { v: :phablet }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "any", @response.body
   end
 
   def test_variant_inline_any_any
     get :variant_inline_any_any, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
 
     get :variant_inline_any_any, params: { v: :yolo }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "any", @response.body
   end
 
   def test_variant_any_implicit_render
     get :variant_any_implicit_render, params: { v: :tablet }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "tablet", @response.body
 
     get :variant_any_implicit_render, params: { v: :phablet }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phablet", @response.body
   end
 
   def test_variant_any_with_none
     get :variant_any_with_none
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "none or phone", @response.body
 
     get :variant_any_with_none, params: { v: :phone }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "none or phone", @response.body
   end
 
   def test_format_any_variant_any
     get :format_any_variant_any, format: :js, params: { v: :tablet }
-    assert_equal "text/javascript", @response.content_type
+    assert_equal "text/javascript", @response.media_type
     assert_equal "tablet", @response.body
   end
 
   def test_variant_negotiation_inline_syntax
     get :variant_inline_syntax_without_block, params: { v: [:tablet, :phone] }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
   end
 
   def test_variant_negotiation_block_syntax
     get :variant_plus_none_for_format, params: { v: [:tablet, :phone] }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
   end
 
   def test_variant_negotiation_without_block
     get :variant_inline_syntax_without_block, params: { v: [:tablet, :phone] }
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
     assert_equal "phone", @response.body
   end
 end
diff --git a/actionpack/test/controller/render_js_test.rb b/actionpack/test/controller/render_js_test.rb
index 1efc0b9de19fe..7ef35c2396214 100644
--- a/actionpack/test/controller/render_js_test.rb
+++ b/actionpack/test/controller/render_js_test.rb
@@ -26,7 +26,7 @@ def show_partial
   def test_render_vanilla_js
     get :render_vanilla_js_hello, xhr: true
     assert_equal "alert('hello')", @response.body
-    assert_equal "text/javascript", @response.content_type
+    assert_equal "text/javascript", @response.media_type
   end
 
   def test_should_render_js_partial
diff --git a/actionpack/test/controller/render_json_test.rb b/actionpack/test/controller/render_json_test.rb
index 82c1ba26cb21b..aba7593c159ae 100644
--- a/actionpack/test/controller/render_json_test.rb
+++ b/actionpack/test/controller/render_json_test.rb
@@ -80,7 +80,7 @@ def setup
   def test_render_json_nil
     get :render_json_nil
     assert_equal "null", @response.body
-    assert_equal "application/json", @response.content_type
+    assert_equal "application/json", @response.media_type
   end
 
   def test_render_json_render_to_string
@@ -91,7 +91,7 @@ def test_render_json_render_to_string
   def test_render_json
     get :render_json_hello_world
     assert_equal '{"hello":"world"}', @response.body
-    assert_equal "application/json", @response.content_type
+    assert_equal "application/json", @response.media_type
   end
 
   def test_render_json_with_status
@@ -103,31 +103,31 @@ def test_render_json_with_status
   def test_render_json_with_callback
     get :render_json_hello_world_with_callback, xhr: true
     assert_equal '/**/alert({"hello":"world"})', @response.body
-    assert_equal "text/javascript", @response.content_type
+    assert_equal "text/javascript", @response.media_type
   end
 
   def test_render_json_with_custom_content_type
     get :render_json_with_custom_content_type, xhr: true
     assert_equal '{"hello":"world"}', @response.body
-    assert_equal "text/javascript", @response.content_type
+    assert_equal "text/javascript", @response.media_type
   end
 
   def test_render_symbol_json
     get :render_symbol_json
     assert_equal '{"hello":"world"}', @response.body
-    assert_equal "application/json", @response.content_type
+    assert_equal "application/json", @response.media_type
   end
 
   def test_render_json_with_render_to_string
     get :render_json_with_render_to_string
     assert_equal '{"hello":"partial html"}', @response.body
-    assert_equal "application/json", @response.content_type
+    assert_equal "application/json", @response.media_type
   end
 
   def test_render_json_forwards_extra_options
     get :render_json_with_extra_options
     assert_equal '{"a":"b"}', @response.body
-    assert_equal "application/json", @response.content_type
+    assert_equal "application/json", @response.media_type
   end
 
   def test_render_json_calls_to_json_from_object
diff --git a/actionpack/test/controller/render_xml_test.rb b/actionpack/test/controller/render_xml_test.rb
index a72d14e4bb3c6..7d61076e7cfd6 100644
--- a/actionpack/test/controller/render_xml_test.rb
+++ b/actionpack/test/controller/render_xml_test.rb
@@ -92,11 +92,11 @@ def test_should_render_formatted_xml_erb_template
 
   def test_should_render_xml_but_keep_custom_content_type
     get :render_xml_with_custom_content_type
-    assert_equal "application/atomsvc+xml", @response.content_type
+    assert_equal "application/atomsvc+xml", @response.media_type
   end
 
   def test_should_use_implicit_content_type
     get :implicit_content_type, format: "atom"
-    assert_equal Mime[:atom], @response.content_type
+    assert_equal Mime[:atom], @response.media_type
   end
 end
diff --git a/actionpack/test/controller/renderers_test.rb b/actionpack/test/controller/renderers_test.rb
index d92de6f5d54d7..96cce664a4c97 100644
--- a/actionpack/test/controller/renderers_test.rb
+++ b/actionpack/test/controller/renderers_test.rb
@@ -73,7 +73,7 @@ def test_raises_missing_template_no_renderer
     assert_raise ActionView::MissingTemplate do
       get :respond_to_mime, format: "csv"
     end
-    assert_equal Mime[:csv], @response.content_type
+    assert_equal Mime[:csv], @response.media_type
     assert_equal "", @response.body
   end
 
@@ -83,7 +83,7 @@ def test_adding_csv_rendering_via_renderers_add
     end
     @request.accept = "text/csv"
     get :respond_to_mime, format: "csv"
-    assert_equal Mime[:csv], @response.content_type
+    assert_equal Mime[:csv], @response.media_type
     assert_equal "c,s,v", @response.body
   ensure
     ActionController::Renderers.remove :csv
diff --git a/actionpack/test/controller/show_exceptions_test.rb b/actionpack/test/controller/show_exceptions_test.rb
index 8724f9bcdbaaa..59acc335e7e42 100644
--- a/actionpack/test/controller/show_exceptions_test.rb
+++ b/actionpack/test/controller/show_exceptions_test.rb
@@ -76,7 +76,7 @@ def test_render_json_exception
       @app = ShowExceptionsOverriddenController.action(:boom)
       get "/", headers: { "HTTP_ACCEPT" => "application/json" }
       assert_response :internal_server_error
-      assert_equal "application/json", response.content_type.to_s
+      assert_equal "application/json", response.media_type
       assert_equal({ status: 500, error: "Internal Server Error" }.to_json, response.body)
     end
 
@@ -84,7 +84,7 @@ def test_render_xml_exception
       @app = ShowExceptionsOverriddenController.action(:boom)
       get "/", headers: { "HTTP_ACCEPT" => "application/xml" }
       assert_response :internal_server_error
-      assert_equal "application/xml", response.content_type.to_s
+      assert_equal "application/xml", response.media_type
       assert_equal({ status: 500, error: "Internal Server Error" }.to_xml, response.body)
     end
 
@@ -92,7 +92,7 @@ def test_render_fallback_exception
       @app = ShowExceptionsOverriddenController.action(:boom)
       get "/", headers: { "HTTP_ACCEPT" => "text/csv" }
       assert_response :internal_server_error
-      assert_equal "text/html", response.content_type.to_s
+      assert_equal "text/html", response.media_type
     end
   end
 
@@ -106,7 +106,7 @@ def test_render_failsafe_exception
 
       get "/", headers: { "HTTP_ACCEPT" => "text/json" }
       assert_response :internal_server_error
-      assert_equal "text/plain", response.content_type.to_s
+      assert_equal "text/plain", response.media_type
     ensure
       middleware.instance_variable_set(:@exceptions_app, @exceptions_app)
       $stderr = STDERR
diff --git a/actionpack/test/dispatch/debug_exceptions_test.rb b/actionpack/test/dispatch/debug_exceptions_test.rb
index 5ae8a20ae4d60..f358e18da872e 100644
--- a/actionpack/test/dispatch/debug_exceptions_test.rb
+++ b/actionpack/test/dispatch/debug_exceptions_test.rb
@@ -208,7 +208,7 @@ def call(env)
     assert_response 500
     assert_no_match(/<header>/, body)
     assert_no_match(/<body>/, body)
-    assert_equal "text/plain", response.content_type
+    assert_equal "text/plain", response.media_type
     assert_match(/RuntimeError\npuke/, body)
 
     Rails.stub :root, Pathname.new(".") do
@@ -222,31 +222,31 @@ def call(env)
     get "/not_found", headers: xhr_request_env
     assert_response 404
     assert_no_match(/<body>/, body)
-    assert_equal "text/plain", response.content_type
+    assert_equal "text/plain", response.media_type
     assert_match(/#{AbstractController::ActionNotFound.name}/, body)
 
     get "/method_not_allowed", headers: xhr_request_env
     assert_response 405
     assert_no_match(/<body>/, body)
-    assert_equal "text/plain", response.content_type
+    assert_equal "text/plain", response.media_type
     assert_match(/ActionController::MethodNotAllowed/, body)
 
     get "/unknown_http_method", headers: xhr_request_env
     assert_response 405
     assert_no_match(/<body>/, body)
-    assert_equal "text/plain", response.content_type
+    assert_equal "text/plain", response.media_type
     assert_match(/ActionController::UnknownHttpMethod/, body)
 
     get "/bad_request", headers: xhr_request_env
     assert_response 400
     assert_no_match(/<body>/, body)
-    assert_equal "text/plain", response.content_type
+    assert_equal "text/plain", response.media_type
     assert_match(/ActionController::BadRequest/, body)
 
     get "/parameter_missing", headers: xhr_request_env
     assert_response 400
     assert_no_match(/<body>/, body)
-    assert_equal "text/plain", response.content_type
+    assert_equal "text/plain", response.media_type
     assert_match(/ActionController::ParameterMissing/, body)
   end
 
@@ -257,37 +257,37 @@ def call(env)
     assert_response 500
     assert_no_match(/<header>/, body)
     assert_no_match(/<body>/, body)
-    assert_equal "application/json", response.content_type
+    assert_equal "application/json", response.media_type
     assert_match(/RuntimeError: puke/, body)
 
     get "/not_found", headers: { "action_dispatch.show_exceptions" => true }, as: :json
     assert_response 404
     assert_no_match(/<body>/, body)
-    assert_equal "application/json", response.content_type
+    assert_equal "application/json", response.media_type
     assert_match(/#{AbstractController::ActionNotFound.name}/, body)
 
     get "/method_not_allowed", headers: { "action_dispatch.show_exceptions" => true }, as: :json
     assert_response 405
     assert_no_match(/<body>/, body)
-    assert_equal "application/json", response.content_type
+    assert_equal "application/json", response.media_type
     assert_match(/ActionController::MethodNotAllowed/, body)
 
     get "/unknown_http_method", headers: { "action_dispatch.show_exceptions" => true }, as: :json
     assert_response 405
     assert_no_match(/<body>/, body)
-    assert_equal "application/json", response.content_type
+    assert_equal "application/json", response.media_type
     assert_match(/ActionController::UnknownHttpMethod/, body)
 
     get "/bad_request", headers: { "action_dispatch.show_exceptions" => true }, as: :json
     assert_response 400
     assert_no_match(/<body>/, body)
-    assert_equal "application/json", response.content_type
+    assert_equal "application/json", response.media_type
     assert_match(/ActionController::BadRequest/, body)
 
     get "/parameter_missing", headers: { "action_dispatch.show_exceptions" => true }, as: :json
     assert_response 400
     assert_no_match(/<body>/, body)
-    assert_equal "application/json", response.content_type
+    assert_equal "application/json", response.media_type
     assert_match(/ActionController::ParameterMissing/, body)
   end
 
@@ -298,7 +298,7 @@ def call(env)
     assert_response 500
     assert_match(/<header>/, body)
     assert_match(/<body>/, body)
-    assert_equal "text/html", response.content_type
+    assert_equal "text/html", response.media_type
     assert_match(/puke/, body)
   end
 
@@ -307,7 +307,7 @@ def call(env)
 
     get "/index.xml", headers: { "action_dispatch.show_exceptions" => true }
     assert_response 500
-    assert_equal "application/xml", response.content_type
+    assert_equal "application/xml", response.media_type
     assert_match(/RuntimeError: puke/, body)
   end
 
@@ -321,7 +321,7 @@ def call(env)
 
     get "/index", headers: { "action_dispatch.show_exceptions" => true }, as: :wibble
     assert_response 500
-    assert_equal "application/json", response.content_type
+    assert_equal "application/json", response.media_type
     assert_match(/RuntimeError: puke/, body)
 
   ensure
diff --git a/actionpack/test/dispatch/response_test.rb b/actionpack/test/dispatch/response_test.rb
index 7758b0406ae95..7d9f34b4d7c6a 100644
--- a/actionpack/test/dispatch/response_test.rb
+++ b/actionpack/test/dispatch/response_test.rb
@@ -112,9 +112,9 @@ def test_setting_content_type_header_impacts_content_type_method
     assert_equal "application/aaron", @response.content_type
   end
 
-  def test_empty_content_type_returns_nil
+  def test_empty_content_type_returns_empty_string
     @response.headers["Content-Type"] = ""
-    assert_nil @response.content_type
+    assert_empty @response.content_type
   end
 
   test "simple output" do
@@ -290,7 +290,7 @@ def test_only_set_charset_still_defaults_to_text_html
     resp.to_a
 
     assert_equal("utf-16", resp.charset)
-    assert_equal(Mime[:xml], resp.content_type)
+    assert_equal(Mime[:xml], resp.media_type)
 
     assert_equal("application/xml; charset=utf-16", resp.headers["Content-Type"])
   end
@@ -503,7 +503,8 @@ class ResponseIntegrationTest < ActionDispatch::IntegrationTest
     assert_response :success
 
     assert_equal("utf-16", @response.charset)
-    assert_equal(Mime[:xml], @response.content_type)
+    assert_equal(Mime[:xml], @response.media_type)
+    assert_equal("application/xml; charset=utf-16", @response.content_type)
 
     assert_equal("application/xml; charset=utf-16", @response.headers["Content-Type"])
   end
@@ -519,7 +520,8 @@ class ResponseIntegrationTest < ActionDispatch::IntegrationTest
     assert_response :success
 
     assert_equal("utf-16", @response.charset)
-    assert_equal(Mime[:xml], @response.content_type)
+    assert_equal(Mime[:xml], @response.media_type)
+    assert_equal("application/xml; charset=utf-16", @response.content_type)
 
     assert_equal("application/xml; charset=utf-16", @response.headers["Content-Type"])
   end
@@ -553,7 +555,26 @@ class ResponseIntegrationTest < ActionDispatch::IntegrationTest
     assert_response :success
 
     assert_equal("text/csv; charset=utf-16; header=present", @response.headers["Content-Type"])
-    assert_equal("text/csv", @response.content_type)
+    assert_equal("text/csv; charset=utf-16; header=present", @response.content_type)
+    assert_equal("text/csv", @response.media_type)
+    assert_equal("utf-16", @response.charset)
+  end
+
+  test "response Content-Type with optional parameters that set before charset" do
+    @app = lambda { |env|
+      [
+        200,
+        { "Content-Type" => "text/csv; header=present; charset=utf-16" },
+        ["Hello"]
+      ]
+    }
+
+    get "/"
+    assert_response :success
+
+    assert_equal("text/csv; header=present; charset=utf-16", @response.headers["Content-Type"])
+    assert_equal("text/csv; header=present; charset=utf-16", @response.content_type)
+    assert_equal("text/csv", @response.media_type)
     assert_equal("utf-16", @response.charset)
   end
 
@@ -570,7 +591,8 @@ class ResponseIntegrationTest < ActionDispatch::IntegrationTest
     assert_response :success
 
     assert_equal('text/csv; header=present; charset="utf-16"', @response.headers["Content-Type"])
-    assert_equal("text/csv", @response.content_type)
+    assert_equal('text/csv; header=present; charset="utf-16"', @response.content_type)
+    assert_equal("text/csv", @response.media_type)
     assert_equal("utf-16", @response.charset)
   end
 end
diff --git a/actionview/test/actionpack/controller/render_test.rb b/actionview/test/actionpack/controller/render_test.rb
index c8ce7366d19da..9b1a720636a17 100644
--- a/actionview/test/actionpack/controller/render_test.rb
+++ b/actionview/test/actionpack/controller/render_test.rb
@@ -1003,14 +1003,14 @@ def test_access_to_controller_name_in_view
   def test_render_xml
     get :render_xml_hello
     assert_equal "<html>\n  <p>Hello David</p>\n<p>This is grand!</p>\n</html>\n", @response.body
-    assert_equal "application/xml", @response.content_type
+    assert_equal "application/xml", @response.media_type
   end
 
   # :ported:
   def test_render_xml_as_string_template
     get :render_xml_hello_as_string_template
     assert_equal "<html>\n  <p>Hello David</p>\n<p>This is grand!</p>\n</html>\n", @response.body
-    assert_equal "application/xml", @response.content_type
+    assert_equal "application/xml", @response.media_type
   end
 
   # :ported:
@@ -1039,7 +1039,7 @@ def test_render_xml_with_layouts
   def test_rendered_format_without_format
     get :inline_rendered_format_without_format
     assert_equal "test", @response.body
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_partials_list
@@ -1077,7 +1077,7 @@ def test_accessing_params_in_template
   def test_accessing_local_assigns_in_inline_template
     get :accessing_local_assigns_in_inline_template, params: { local_name: "Local David" }
     assert_equal "Goodbye, Local David", @response.body
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_should_implicitly_render_html_template_from_xhr_request
@@ -1264,13 +1264,13 @@ def test_using_layout_around_block_in_main_layout_and_within_content_for_layout
   def test_partial_only
     get :partial_only
     assert_equal "only partial", @response.body
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_should_render_html_formatted_partial
     get :partial
     assert_equal "partial html", @response.body
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_render_html_formatted_partial_even_with_other_mime_time_in_accept
@@ -1279,20 +1279,20 @@ def test_render_html_formatted_partial_even_with_other_mime_time_in_accept
     get :partial_html_erb
 
     assert_equal "partial.html.erb", @response.body.strip
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_should_render_html_partial_with_formats
     get :partial_formats_html
     assert_equal "partial html", @response.body
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_render_to_string_partial
     get :render_to_string_with_partial
     assert_equal "only partial", @controller.instance_variable_get(:@partial_only)
     assert_equal "Hello: david", @controller.instance_variable_get(:@partial_with_locals)
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_render_to_string_with_template_and_html_partial
@@ -1300,21 +1300,21 @@ def test_render_to_string_with_template_and_html_partial
     assert_equal "**only partial**\n", @controller.instance_variable_get(:@text)
     assert_equal "<strong>only partial</strong>\n", @controller.instance_variable_get(:@html)
     assert_equal "<strong>only html partial</strong>\n", @response.body
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_render_to_string_and_render_with_different_formats
     get :render_to_string_and_render_with_different_formats
     assert_equal "<strong>only partial</strong>\n", @controller.instance_variable_get(:@html)
     assert_equal "**only partial**\n", @response.body
-    assert_equal "text/plain", @response.content_type
+    assert_equal "text/plain", @response.media_type
   end
 
   def test_render_template_within_a_template_with_other_format
     get :render_template_within_a_template_with_other_format
     expected = "only html partial<p>This is grand!</p>"
     assert_equal expected, @response.body.strip
-    assert_equal "text/html", @response.content_type
+    assert_equal "text/html", @response.media_type
   end
 
   def test_partial_with_counter