diff --git a/Gemfile b/Gemfile
index c720b09a2c..0b6de3061f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -15,6 +15,8 @@ gem "sprockets", :git => "git://github.com/sstephenson/sprockets.git"
 gem "coffee-script"
 gem "sass", ">= 3.0"
 
+gem "multi_json", :git => 'git://github.com/intridea/multi_json.git'
+
 gem "rake",  ">= 0.8.7"
 gem "mocha", ">= 0.9.8"
 
diff --git a/activesupport/lib/active_support/json/backends/jsongem.rb b/activesupport/lib/active_support/json/backends/jsongem.rb
deleted file mode 100644
index 533ba25da3..0000000000
--- a/activesupport/lib/active_support/json/backends/jsongem.rb
+++ /dev/null
@@ -1,47 +0,0 @@
-require 'json' unless defined?(JSON)
-
-module ActiveSupport
-  module JSON
-    module Backends
-      module JSONGem
-        ParseError = ::JSON::ParserError
-        extend self
-
-        # Parses a JSON string or IO and convert it into an object
-        def decode(json)
-          if json.respond_to?(:read)
-            json = json.read
-          end
-          data = ::JSON.parse(json)
-          if ActiveSupport.parse_json_times
-            convert_dates_from(data)
-          else
-            data
-          end
-        end
-
-      private
-        def convert_dates_from(data)
-          case data
-          when nil
-            nil
-          when DATE_REGEX
-            begin
-              DateTime.parse(data)
-            rescue ArgumentError
-              data
-            end
-          when Array
-            data.map! { |d| convert_dates_from(d) }
-          when Hash
-            data.each do |key, value|
-              data[key] = convert_dates_from(value)
-            end
-          else
-            data
-          end
-        end
-      end
-    end
-  end
-end
diff --git a/activesupport/lib/active_support/json/backends/yajl.rb b/activesupport/lib/active_support/json/backends/yajl.rb
deleted file mode 100644
index 58818658c7..0000000000
--- a/activesupport/lib/active_support/json/backends/yajl.rb
+++ /dev/null
@@ -1,44 +0,0 @@
-require 'yajl' unless defined?(Yajl)
-
-module ActiveSupport
-  module JSON
-    module Backends
-      module Yajl
-        ParseError = ::Yajl::ParseError
-        extend self
-
-        # Parses a JSON string or IO and convert it into an object
-        def decode(json)
-          data = ::Yajl::Parser.new.parse(json)
-          if ActiveSupport.parse_json_times
-            convert_dates_from(data)
-          else
-            data
-          end
-        end
-
-      private
-        def convert_dates_from(data)
-          case data
-          when nil
-            nil
-          when DATE_REGEX
-            begin
-              DateTime.parse(data)
-            rescue ArgumentError
-              data
-            end
-          when Array
-            data.map! { |d| convert_dates_from(d) }
-          when Hash
-            data.each do |key, value|
-              data[key] = convert_dates_from(value)
-            end
-          else
-            data
-          end
-        end
-      end
-    end
-  end
-end
diff --git a/activesupport/lib/active_support/json/backends/yaml.rb b/activesupport/lib/active_support/json/backends/yaml.rb
deleted file mode 100644
index e25e29d36b..0000000000
--- a/activesupport/lib/active_support/json/backends/yaml.rb
+++ /dev/null
@@ -1,113 +0,0 @@
-require 'active_support/core_ext/string/starts_ends_with'
-
-module ActiveSupport
-  module JSON
-    module Backends
-      module Yaml
-        ParseError = ::StandardError
-        extend self
-
-        EXCEPTIONS = [::ArgumentError] # :nodoc:
-        begin
-          require 'psych'
-          EXCEPTIONS << Psych::SyntaxError
-        rescue LoadError
-        end
-
-        # Parses a JSON string or IO and converts it into an object
-        def decode(json)
-          if json.respond_to?(:read)
-            json = json.read
-          end
-          YAML.load(convert_json_to_yaml(json))
-        rescue *EXCEPTIONS => e
-          raise ParseError, "Invalid JSON string: '%s'" % json
-        end
-
-        protected
-          # Ensure that ":" and "," are always followed by a space
-          def convert_json_to_yaml(json) #:nodoc:
-            require 'strscan' unless defined? ::StringScanner
-            scanner, quoting, marks, pos, times = ::StringScanner.new(json), false, [], nil, []
-            while scanner.scan_until(/(\\['"]|['":,\\]|\\.|[\]])/)
-              case char = scanner[1]
-              when '"', "'"
-                if !quoting
-                  quoting = char
-                  pos = scanner.pos
-                elsif quoting == char
-                  if valid_date?(json[pos..scanner.pos-2])
-                    # found a date, track the exact positions of the quotes so we can
-                    # overwrite them with spaces later.
-                    times << pos
-                  end
-                  quoting = false
-                end
-              when ":",",", "]"
-                marks << scanner.pos - 1 unless quoting
-              when "\\"
-                scanner.skip(/\\/)
-              end
-            end
-
-            if marks.empty?
-              json.gsub(/\\([\\\/]|u[[:xdigit:]]{4})/) do
-                ustr = $1
-                if ustr.start_with?('u')
-                  char = [ustr[1..-1].to_i(16)].pack("U")
-                  # "\n" needs extra escaping due to yaml formatting
-                  char == "\n" ? "\\n" : char
-                elsif ustr == '\\'
-                  '\\\\'
-                else
-                  ustr
-                end
-              end
-            else
-              left_pos  = [-1].push(*marks)
-              right_pos = marks << scanner.pos + scanner.rest_size
-              output    = []
-              left_pos.each_with_index do |left, i|
-                scanner.pos = left.succ
-                chunk = scanner.peek(right_pos[i] - scanner.pos + 1)
-                if ActiveSupport.parse_json_times
-                  # overwrite the quotes found around the dates with spaces
-                  while times.size > 0 && times[0] <= right_pos[i]
-                    chunk.insert(times.shift - scanner.pos - 1, '! ')
-                  end
-                end
-                chunk.gsub!(/\\([\\\/]|u[[:xdigit:]]{4})/) do
-                  ustr = $1
-                  if ustr.start_with?('u')
-                    char = [ustr[1..-1].to_i(16)].pack("U")
-                    # "\n" needs extra escaping due to yaml formatting
-                    char == "\n" ? "\\n" : char
-                  elsif ustr == '\\'
-                    '\\\\'
-                  else
-                    ustr
-                  end
-                end
-                output << chunk
-              end
-              output = output * " "
-
-              output.gsub!(/\\\//, '/')
-              output
-            end
-          end
-
-        private
-          def valid_date?(date_string)
-            begin
-              date_string =~ DATE_REGEX && DateTime.parse(date_string)
-            rescue ArgumentError
-              false
-            end
-          end
-
-      end
-    end
-  end
-end
-
diff --git a/activesupport/lib/active_support/json/decoding.rb b/activesupport/lib/active_support/json/decoding.rb
index c1f6330c6c..ac99f180a5 100644
--- a/activesupport/lib/active_support/json/decoding.rb
+++ b/activesupport/lib/active_support/json/decoding.rb
@@ -1,33 +1,32 @@
 require 'active_support/core_ext/module/attribute_accessors'
 require 'active_support/core_ext/module/delegation'
+require 'multi_json'
 
 module ActiveSupport
   # Look for and parse json strings that look like ISO 8601 times.
   mattr_accessor :parse_json_times
 
   module JSON
-    # Listed in order of preference.
-    DECODERS = %w(Yajl Yaml)
-
     class << self
-      attr_reader :parse_error
-      delegate :decode, :to => :backend
-
-      def backend
-        set_default_backend unless defined?(@backend)
-        @backend
-      end
-
-      def backend=(name)
-        if name.is_a?(Module)
-          @backend = name
+      def decode(json, options ={})
+        data = MultiJson.decode(json, options)
+        if ActiveSupport.parse_json_times
+          convert_dates_from(data)
         else
-          require "active_support/json/backends/#{name.to_s.downcase}"
-          @backend = ActiveSupport::JSON::Backends::const_get(name)
+          data
         end
-        @parse_error = @backend::ParseError
       end
 
+      def engine
+        MultiJson.engine
+      end
+      alias :backend :engine
+
+      def engine=(name)
+        MultiJson.engine = name
+      end
+      alias :backend= :engine=
+
       def with_backend(name)
         old_backend, self.backend = backend, name
         yield
@@ -35,15 +34,26 @@ module ActiveSupport
         self.backend = old_backend
       end
 
-      def set_default_backend
-        DECODERS.find do |name|
+      private
+
+      def convert_dates_from(data)
+        case data
+        when nil
+          nil
+        when DATE_REGEX
           begin
-            self.backend = name
-            true
-          rescue LoadError
-            # Try next decoder.
-            false
+            DateTime.parse(data)
+          rescue ArgumentError
+            data
           end
+        when Array
+          data.map! { |d| convert_dates_from(d) }
+        when Hash
+          data.each do |key, value|
+            data[key] = convert_dates_from(value)
+          end
+        else
+          data
         end
       end
     end
diff --git a/activesupport/test/json/decoding_test.rb b/activesupport/test/json/decoding_test.rb
index 88cf97de7e..0e6772e284 100644
--- a/activesupport/test/json/decoding_test.rb
+++ b/activesupport/test/json/decoding_test.rb
@@ -56,12 +56,9 @@ class TestJSONDecoding < ActiveSupport::TestCase
     %q({"a":"Line1\u000aLine2"}) => {"a"=>"Line1\nLine2"}
   }
 
-  # load the default JSON backend
-  ActiveSupport::JSON.backend = 'Yaml'
-
-  backends = %w(Yaml)
-  backends << "JSONGem" if defined?(::JSON)
-  backends << "Yajl" if defined?(::Yajl)
+  backends = [:ok_json]
+  backends << :json_gem if defined?(::JSON)
+  backends << :yajl if defined?(::Yajl)
 
   backends.each do |backend|
     TESTS.each do |json, expected|
@@ -85,7 +82,7 @@ class TestJSONDecoding < ActiveSupport::TestCase
   end
 
   def test_failed_json_decoding
-    assert_raise(ActiveSupport::JSON.parse_error) { ActiveSupport::JSON.decode(%({: 1})) }
+    assert_raise(MultiJson::DecodeError) { ActiveSupport::JSON.decode(%({: 1})) }
   end
 end