diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 4b5657a57955b..669732a148a3c 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Prefer MIME constants to strings.  #7707 [Dan Kubb]
+
 * Allow array and hash query parameters. Array route parameters are converted/to/a/path as before.  #6765, #7047, #7462 [bgipsy, Jeremy McAnally, Dan Kubb, brendan]
 
 # Add a #dbman attr_reader for CGI::Session and make CGI::Session::CookieStore#generate_digest public so it's easy to generate digests
diff --git a/actionpack/lib/action_controller/deprecated_request_methods.rb b/actionpack/lib/action_controller/deprecated_request_methods.rb
index a6cf87e358886..93663bdda4063 100644
--- a/actionpack/lib/action_controller/deprecated_request_methods.rb
+++ b/actionpack/lib/action_controller/deprecated_request_methods.rb
@@ -6,10 +6,10 @@ class AbstractRequest
     # For backward compatibility, the post format is extracted from the
     # X-Post-Data-Format HTTP header if present.
     def post_format
-      case content_type.to_s
-      when 'application/xml'
+      case content_type
+      when Mime::XML
         :xml
-      when 'application/x-yaml'
+      when Mime::YAML
         :yaml
       else
         :url_encoded
diff --git a/actionpack/lib/action_controller/mime_type.rb b/actionpack/lib/action_controller/mime_type.rb
index 17b3d861ec47d..b179fe2f892e4 100644
--- a/actionpack/lib/action_controller/mime_type.rb
+++ b/actionpack/lib/action_controller/mime_type.rb
@@ -24,7 +24,7 @@ class AcceptItem #:nodoc:
       def initialize(order, name, q=nil)
         @order = order
         @name = name.strip
-        q ||= 0.0 if @name == "*/*" # default "*/*" to end of list
+        q ||= 0.0 if @name == Mime::ALL # default wilcard match to end of list
         @q = ((q || 1.0).to_f * 100).to_i
       end
 
@@ -70,7 +70,7 @@ def parse(accept_header)
 
         # Take care of the broken text/xml entry by renaming or deleting it
         text_xml = list.index("text/xml")
-        app_xml = list.index("application/xml")
+        app_xml = list.index(Mime::XML.to_s)
 
         if text_xml && app_xml
           # set the q value to the max of the two
@@ -84,9 +84,9 @@ def parse(accept_header)
 
           # delete text_xml from the list
           list.delete_at(text_xml)
-  
+
         elsif text_xml
-          list[text_xml].name = "application/xml"
+          list[text_xml].name = Mime::XML.to_s
         end
 
         # Look for more specific xml-based types and sort them ahead of app/xml
diff --git a/actionpack/lib/action_controller/request.rb b/actionpack/lib/action_controller/request.rb
index 38584a6481c26..cd80415f8295e 100755
--- a/actionpack/lib/action_controller/request.rb
+++ b/actionpack/lib/action_controller/request.rb
@@ -60,16 +60,16 @@ def content_type
         begin
           # Receive header sans any charset information.
           content_type = @env['CONTENT_TYPE'].to_s.sub(/\s*\;.*$/, '').strip.downcase
-          
+
           if x_post_format = @env['HTTP_X_POST_DATA_FORMAT']
             case x_post_format.to_s.downcase
             when 'yaml'
-              content_type = 'application/x-yaml'
+              content_type = Mime::YAML.to_s
             when 'xml'
-              content_type = 'application/xml'
+              content_type = Mime::XML.to_s
             end
           end
-          
+
           Mime::Type.lookup(content_type)
         end
     end
diff --git a/actionpack/lib/action_controller/response.rb b/actionpack/lib/action_controller/response.rb
index 38647670f2f2a..429b3eff3210f 100755
--- a/actionpack/lib/action_controller/response.rb
+++ b/actionpack/lib/action_controller/response.rb
@@ -20,7 +20,7 @@ def content_type
     end
     
     def charset=(encoding)
-      self.headers["Content-Type"] = "#{content_type || "text/html"}; charset=#{encoding}"
+      self.headers["Content-Type"] = "#{content_type || Mime::HTML}; charset=#{encoding}"
     end
     
     def charset
diff --git a/actionpack/lib/action_controller/test_process.rb b/actionpack/lib/action_controller/test_process.rb
index beccec6f94459..b1eb9e38ef3a1 100644
--- a/actionpack/lib/action_controller/test_process.rb
+++ b/actionpack/lib/action_controller/test_process.rb
@@ -325,29 +325,29 @@ def close
   class TestUploadedFile
     # The filename, *not* including the path, of the "uploaded" file
     attr_reader :original_filename
-    
+
     # The content type of the "uploaded" file
     attr_reader :content_type
-    
-    def initialize(path, content_type = 'text/plain')
+
+    def initialize(path, content_type = Mime::TEXT)
       raise "#{path} file does not exist" unless File.exist?(path)
       @content_type = content_type
       @original_filename = path.sub(/^.*#{File::SEPARATOR}([^#{File::SEPARATOR}]+)$/) { $1 }
       @tempfile = Tempfile.new(@original_filename)
       FileUtils.copy_file(path, @tempfile.path)
     end
-    
+
     def path #:nodoc:
       @tempfile.path
     end
-    
+
     alias local_path path
-    
+
     def method_missing(method_name, *args, &block) #:nodoc:
       @tempfile.send(method_name, *args, &block)
     end
   end
-  
+
   module TestProcess
     def self.included(base)
       # execute the request simulating a specific http method and set/volley the response
diff --git a/actionpack/lib/action_view/base.rb b/actionpack/lib/action_view/base.rb
index 1b3cf5d95ebf8..d66b43cd68a16 100644
--- a/actionpack/lib/action_view/base.rb
+++ b/actionpack/lib/action_view/base.rb
@@ -470,11 +470,11 @@ def create_template_source(extension, template, render_symbol, locals)
         if template_requires_setup?(extension)
           body = case extension.to_sym
             when :rxml, :builder
-              "controller.response.content_type ||= 'application/xml'\n" +
+              "controller.response.content_type ||= Mime::XML\n" +
               "xml = Builder::XmlMarkup.new(:indent => 2)\n" +
               template
             when :rjs
-              "controller.response.content_type ||= 'text/javascript'\n" +
+              "controller.response.content_type ||= Mime::JS\n" +
               "update_page do |page|\n#{template}\nend"
           end
         else
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helper.rb b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
index 93e695ddbb30f..8b9e4094ce1e1 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
@@ -149,19 +149,19 @@ def javascript_include_tag(*sources)
           if !File.exists?(joined_javascript_path)
             File.open(joined_javascript_path, "w+") do |cache|
               javascript_paths = expand_javascript_sources(sources).collect do |source|
-                compute_public_path(source, 'javascripts', 'js', false) 
+                compute_public_path(source, 'javascripts', 'js', false)
               end
 
               cache.write(join_asset_file_contents(javascript_paths))
             end
           end
 
-          content_tag("script", "", { 
-            "type" => "text/javascript", "src" => javascript_path(joined_javascript_name)
+          content_tag("script", "", {
+            "type" => Mime::JS, "src" => javascript_path(joined_javascript_name)
           }.merge(options))
         else
           expand_javascript_sources(sources).collect do |source|
-            content_tag("script", "", { "type" => "text/javascript", "src" => javascript_path(source) }.merge(options))
+            content_tag("script", "", { "type" => Mime::JS, "src" => javascript_path(source) }.merge(options))
           end.join("\n")
         end
       end
@@ -252,15 +252,15 @@ def stylesheet_link_tag(*sources)
           end
 
           tag("link", {
-            "rel" => "Stylesheet", "type" => "text/css", "media" => "screen",
+            "rel" => "Stylesheet", "type" => Mime::CSS, "media" => "screen",
             "href" => stylesheet_path(joined_stylesheet_name)
           }.merge(options))
         else
           options.delete("cache")
 
           expand_stylesheet_sources(sources).collect do |source|
-            tag("link", { 
-              "rel" => "Stylesheet", "type" => "text/css", "media" => "screen", "href" => stylesheet_path(source)
+            tag("link", {
+              "rel" => "Stylesheet", "type" => Mime::CSS, "media" => "screen", "href" => stylesheet_path(source)
             }.merge(options))
           end.join("\n")
         end
diff --git a/actionpack/lib/action_view/helpers/java_script_macros_helper.rb b/actionpack/lib/action_view/helpers/java_script_macros_helper.rb
index 6304a1a8b2f2a..0d9e87fba0883 100644
--- a/actionpack/lib/action_view/helpers/java_script_macros_helper.rb
+++ b/actionpack/lib/action_view/helpers/java_script_macros_helper.rb
@@ -198,10 +198,10 @@ def text_field_with_auto_complete(object, method, tag_options = {}, completion_o
         content_tag("div", "", :id => "#{object}_#{method}_auto_complete", :class => "auto_complete") +
         auto_complete_field("#{object}_#{method}", { :url => { :action => "auto_complete_for_#{object}_#{method}" } }.update(completion_options))
       end
-      
+
       private
         def auto_complete_stylesheet
-          content_tag('style', <<-EOT, :type => 'text/css')
+          content_tag('style', <<-EOT, :type => Mime::CSS)
             div.auto_complete {
               width: 350px;
               background: #fff;
@@ -217,17 +217,17 @@ def auto_complete_stylesheet
               margin:0;
               padding:3px;
             }
-            div.auto_complete ul li.selected { 
-              background-color: #ffb; 
+            div.auto_complete ul li.selected {
+              background-color: #ffb;
             }
-            div.auto_complete ul strong.highlight { 
+            div.auto_complete ul strong.highlight {
               color: #800; 
               margin:0;
               padding:0;
             }
           EOT
         end
-      
+
     end
   end
 end
diff --git a/actionpack/lib/action_view/helpers/javascript_helper.rb b/actionpack/lib/action_view/helpers/javascript_helper.rb
index ad74a85584f69..4dd78543678bd 100644
--- a/actionpack/lib/action_view/helpers/javascript_helper.rb
+++ b/actionpack/lib/action_view/helpers/javascript_helper.rb
@@ -132,7 +132,7 @@ def button_to_function(name, *args, &block)
       # public/javascripts/ directory, and use +javascript_include_tag+ to 
       # create remote <script> links.
       def define_javascript_functions
-        javascript = '<script type="text/javascript">'
+        javascript = "<script type=\"#{Mime::JS}\">"
         
         # load prototype.js and its extensions first 
         prototype_libs = Dir.glob(File.join(JAVASCRIPT_PATH, 'prototype*')).sort.reverse
@@ -166,7 +166,7 @@ def escape_javascript(javascript)
       # +html_options+ may be a hash of attributes for the <script> tag. Example:
       #   javascript_tag "alert('All is good')", :defer => 'true' # => <script defer="true" type="text/javascript">alert('All is good')</script>
       def javascript_tag(content, html_options = {})
-        content_tag("script", javascript_cdata_section(content), html_options.merge(:type => "text/javascript"))
+        content_tag("script", javascript_cdata_section(content), html_options.merge(:type => Mime::JS))
       end
 
       def javascript_cdata_section(content) #:nodoc:
diff --git a/actionpack/lib/action_view/helpers/url_helper.rb b/actionpack/lib/action_view/helpers/url_helper.rb
index 688790094b0b1..dc9154dea5cad 100644
--- a/actionpack/lib/action_view/helpers/url_helper.rb
+++ b/actionpack/lib/action_view/helpers/url_helper.rb
@@ -295,7 +295,7 @@ def mail_to(email_address, name = nil, html_options = {})
           for i in 0...tmp.length
             string << sprintf("%%%x",tmp[i])
           end
-          "<script type=\"text/javascript\">eval(unescape('#{string}'))</script>"
+          "<script type=\"#{Mime::JS}\">eval(unescape('#{string}'))</script>"
         elsif encode == "hex"
           email_address_encoded = ''
           email_address_obfuscated.each_byte do |c|