diff --git a/lib/jekyll.rb b/lib/jekyll.rb
index 941084d5..26c6e569 100644
--- a/lib/jekyll.rb
+++ b/lib/jekyll.rb
@@ -76,6 +76,15 @@ require 'jekyll-sass-converter'
 SafeYAML::OPTIONS[:suppress_warnings] = true
 
 module Jekyll
+
+  # Public: Tells you which Jekyll environment you are building in so you can skip tasks
+  # if you need to.  This is useful when doing expensive compression tasks on css and
+  # images and allows you to skip that when working in development.
+
+  def self.env
+    ENV["JEKYLL_ENV"] || "development"
+  end
+
   # Public: Generate a Jekyll configuration Hash by merging the default
   # options with anything in _config.yml, and adding the given options on top.
   #
diff --git a/lib/jekyll/site.rb b/lib/jekyll/site.rb
index 5f1580bb..9efe2500 100644
--- a/lib/jekyll/site.rb
+++ b/lib/jekyll/site.rb
@@ -314,19 +314,23 @@ module Jekyll
     #   "tags"       - The Hash of tag values and Posts.
     #                  See Site#post_attr_hash for type info.
     def site_payload
-      {"jekyll" => { "version" => Jekyll::VERSION },
-       "site"   => Utils.deep_merge_hashes(config,
-         Utils.deep_merge_hashes(Hash[collections.map{|label, coll| [label, coll.docs]}], {
-          "time"         => time,
-          "posts"        => posts.sort { |a, b| b <=> a },
-          "pages"        => pages,
-          "static_files" => static_files.sort { |a, b| a.relative_path <=> b.relative_path },
-          "html_pages"   => pages.reject { |page| !page.html? },
-          "categories"   => post_attr_hash('categories'),
-          "tags"         => post_attr_hash('tags'),
-          "collections"  => collections,
-          "documents"    => documents,
-          "data"         => site_data
+      {
+        "jekyll" => {
+          "version" => Jekyll::VERSION,
+          "environment" => Jekyll.env
+        },
+        "site"   => Utils.deep_merge_hashes(config,
+          Utils.deep_merge_hashes(Hash[collections.map{|label, coll| [label, coll.docs]}], {
+            "time"         => time,
+            "posts"        => posts.sort { |a, b| b <=> a },
+            "pages"        => pages,
+            "static_files" => static_files.sort { |a, b| a.relative_path <=> b.relative_path },
+            "html_pages"   => pages.reject { |page| !page.html? },
+            "categories"   => post_attr_hash('categories'),
+            "tags"         => post_attr_hash('tags'),
+            "collections"  => collections,
+            "documents"    => documents,
+            "data"         => site_data
         }))
       }
     end
diff --git a/test/source/environment.html b/test/source/environment.html
new file mode 100644
index 00000000..b875a61f
--- /dev/null
+++ b/test/source/environment.html
@@ -0,0 +1,5 @@
+---
+title: I'm a Jekyll environment exchequer
+---
+
+{{ jekyll.environment }}
diff --git a/test/test_filters.rb b/test/test_filters.rb
index fc09a850..f2480267 100644
--- a/test/test_filters.rb
+++ b/test/test_filters.rb
@@ -156,7 +156,7 @@ class TestFilters < Test::Unit::TestCase
             assert_equal 2, g["items"].size
           when ""
             assert g["items"].is_a?(Array), "The list of grouped items for '' is not an Array."
-            assert_equal 10, g["items"].size
+            assert_equal 11, g["items"].size
           end
         end
       end
diff --git a/test/test_site.rb b/test/test_site.rb
index 94263491..de02b8dd 100644
--- a/test/test_site.rb
+++ b/test/test_site.rb
@@ -166,6 +166,7 @@ class TestSite < Test::Unit::TestCase
         coffeescript.coffee
         contacts.html
         deal.with.dots.html
+        environment.html
         exploit.md
         foo.md
         index.html
@@ -407,5 +408,35 @@ class TestSite < Test::Unit::TestCase
       end
 
     end
+
+    context "manipulating the Jekyll environment" do
+      setup do
+        @site = Site.new(site_configuration)
+        @site.process
+        @page = @site.pages.find { |p| p.name == "environment.html" }
+      end
+
+      should "default to 'development'" do
+        assert_equal "development", @page.content.strip
+      end
+
+      context "in production" do
+        setup do
+          ENV["JEKYLL_ENV"] = "production"
+          @site = Site.new(site_configuration)
+          @site.process
+          @page = @site.pages.find { |p| p.name == "environment.html" }
+        end
+
+        teardown do
+          ENV.delete("JEKYLL_ENV")
+        end
+
+        should "be overridden by JEKYLL_ENV" do
+          assert_equal "production", @page.content.strip
+        end
+      end
+    end
+
   end
 end