diff --git a/CHANGELOG.md b/CHANGELOG.md
index ff06c85..87bdaf4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # next release
 
 * The admin interface now supports bookmarks for quickly creating drafts. Selected text on the page will be turned into Markdown. (#50)
+* Posts with a header of `update: now` will have their `Updated` timestamps updated automatically on the next generate. (#49)
 * The 'markdown' filter now properly turns single quotes in Markdown into curly quotes. (#40)
 * Add `archive_page` template flag set to true when processing archive pages. (#41)
 * Make the `month` archive variable available to layouts as well as the archive template. (#41)
diff --git a/Gemfile.lock b/Gemfile.lock
index 1449a67..efce25f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -3,6 +3,7 @@ PATH
   specs:
     serif (0.3.3)
       liquid (~> 2.4)
+      nokogiri (~> 1.5)
       rack (~> 1.0)
       redcarpet (~> 2.2)
       redhead (~> 0.0.8)
@@ -17,14 +18,14 @@ GEM
     diff-lcs (1.1.3)
     liquid (2.5.0)
     multi_json (1.6.1)
-    nokogiri (1.5.5)
+    nokogiri (1.5.6)
     rack (1.5.2)
     rack-protection (1.5.0)
       rack
     rake (0.9.6)
     redcarpet (2.2.2)
     redhead (0.0.8)
-    reverse_markdown (0.4.3)
+    reverse_markdown (0.4.4)
       nokogiri
     rouge (0.3.2)
       thor
@@ -45,8 +46,8 @@ GEM
       rack-protection (~> 1.4)
       tilt (~> 1.3, >= 1.3.4)
     thor (0.17.0)
-    tilt (1.3.5)
-    timecop (0.5.9.2)
+    tilt (1.3.6)
+    timecop (0.6.1)
     timeout_cache (0.0.2)
 
 PLATFORMS
@@ -57,4 +58,4 @@ DEPENDENCIES
   rspec (~> 2.5)
   serif!
   simplecov (~> 0.7)
-  timecop (~> 0.5.5)
+  timecop (~> 0.6.1)
diff --git a/README.md b/README.md
index 454e3ea..d20d40c 100644
--- a/README.md
+++ b/README.md
@@ -30,11 +30,12 @@ Now visit <http://localhost:8000/> to view the site.
 * [Basic usage](#basics)
 * [Content and site structure](#content-and-site-structure)
 * [Publishing drafts](#publishing-drafts)
+* [Updating posts](#updating-posts)
 * [Archive pages](#archive-pages)
 * [Configuration](#configuration)
 * [Deploying](#deploying)
 * [Customising the admin interface](#customising-the-admin-interface)
-* [Custom tags](#custom-tags)
+* [Custom tags and filters](#custom-tags-and-filters)
 * [Template variables](#template-variables)
 * [Developing Serif](#developing-serif)
 * [Changes and what's new](#changes-and-whats-new)
@@ -280,6 +281,26 @@ This is a draft that will be published now.
 
 On the next site generation (`serif generate`) this draft will be automatically published, using the current time as the creation timestamp.
 
+# Updating posts
+
+When you update a draft, you need to remember to change the updated time. As luck would have it, Serif takes care of timestamps for you! Just use a header of `update: now` at the top of your post:
+
+```
+title: My blog post
+Created: 2013-01-01T12:01:30+00:00
+update: now
+```
+
+Now the next time the site is generated, the timestamp will be updated:
+
+```
+title: My blog post
+Created: 2013-01-01T12:01:30+00:00
+Updated: 2013-03-18T19:03:30+00:00
+```
+
+Admin users: this is all done for you.
+
 # Archive pages
 
 By default, archive pages are made available at `/archive/:year/month`, e.g., `/archive/2012/11`. Individual archive pages can be customised by editing the `_templates/archive_page.html` file, which is used for each month.
diff --git a/lib/serif/content_file.rb b/lib/serif/content_file.rb
index 0977e10..ee20a43 100644
--- a/lib/serif/content_file.rb
+++ b/lib/serif/content_file.rb
@@ -122,11 +122,18 @@ def inspect
 
   def set_publish_time(time)
     @source.headers[:created] = time.xmlschema
-    @cached_headers = nil
+    headers_changed!
   end
 
   def set_updated_time(time)
     @source.headers[:updated] = time.xmlschema
+    headers_changed!
+  end
+
+  # Invalidates the cached headers entirely.
+  #
+  # Any methods which alter headers should call this.
+  def headers_changed!
     @cached_headers = nil
   end
 
diff --git a/lib/serif/draft.rb b/lib/serif/draft.rb
index f33d64e..56eadfa 100644
--- a/lib/serif/draft.rb
+++ b/lib/serif/draft.rb
@@ -36,18 +36,16 @@ def publish!
     @path = Post.from_slug(site, slug).path
   end
 
-  # sets the autopublish flag to the given value.
-  #
   # if the assigned value is truthy, the "publish" header
   # is set to "now", otherwise the header is removed.
   def autopublish=(value)
-    @autopublish = value
-
     if value
       @source.headers[:publish] = "now"
     else
       @source.headers.delete(:publish)
     end
+
+    headers_changed!
   end
 
   # Checks the value of the "publish" header, and returns
diff --git a/lib/serif/post.rb b/lib/serif/post.rb
index 74fb1f8..81121c4 100755
--- a/lib/serif/post.rb
+++ b/lib/serif/post.rb
@@ -27,6 +27,36 @@ def url
     output
   end
 
+  # if the assigned value is truthy, the "update" header
+  # is set to "now", otherwise the header is removed.
+  def autoupdate=(value)
+    if value
+      @source.headers[:update] = "now"
+    else
+      @source.headers.delete(:update)
+    end
+
+    headers_changed!
+  end
+
+  # returns true if the post has been marked as needing a
+  # new updated timestamp header.
+  #
+  # this is based on the presence of an "update: now" header.
+  def autoupdate?
+    update_header = headers[:update]
+    update_header && update_header.strip == "now"
+  end
+
+  # Updates the updated timestamp and saves the contents.
+  #
+  # If there is an "update" header (see autoupdate?), it is deleted.
+  def update!
+    @source.headers.delete(:update)
+    set_updated_time(Time.now)
+    save
+  end
+
   def self.all(site)
     files = Dir[File.join(site.directory, dirname, "*")].select { |f| File.file?(f) }.map { |f| File.expand_path(f) }
     files.map { |f| new(site, f) }
diff --git a/lib/serif/site.rb b/lib/serif/site.rb
index a418982..ffb05d2 100644
--- a/lib/serif/site.rb
+++ b/lib/serif/site.rb
@@ -253,6 +253,9 @@ def generate
     # to operate on.
     preprocess_autopublish_drafts
 
+    # preprocess any posts that might have had an update flag set in the header
+    preprocess_autoupdate_posts
+
     posts = self.posts
 
     files.each do |path|
@@ -346,6 +349,15 @@ def generate
 
   private
 
+  def preprocess_autoupdate_posts
+    posts.each do |p|
+      if p.autoupdate?
+        puts "Auto-updating timestamp for: #{p.title} / #{p.slug}"
+        p.update!
+      end
+    end
+  end
+
   # generates draft preview files for any unpublished drafts.
   #
   # uses the same template as live posts.
diff --git a/serif.gemspec b/serif.gemspec
index 9bf84b8..8b181e3 100644
--- a/serif.gemspec
+++ b/serif.gemspec
@@ -29,5 +29,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency("rake", "~> 0.9")
   s.add_development_dependency("rspec", "~> 2.5")
   s.add_development_dependency("simplecov", "~> 0.7")
-  s.add_development_dependency("timecop", "~> 0.5.5")
+  s.add_development_dependency("timecop", "~> 0.6.1")
 end
diff --git a/test/draft_spec.rb b/test/draft_spec.rb
index e992e30..2db46f1 100644
--- a/test/draft_spec.rb
+++ b/test/draft_spec.rb
@@ -152,6 +152,20 @@
 
       draft.delete!
     end
+
+    it "carries its value through to #autopublish?" do
+      draft = D.new(@site)
+      draft.slug = "test-draft"
+      draft.title = "Some draft title"
+      draft.autopublish = false
+      draft.autopublish?.should be_false
+
+      draft.autopublish = true
+      draft.autopublish?.should be_true
+
+      draft.autopublish = false
+      draft.autopublish?.should be_false
+    end
   end
 
   describe "#autopublish?" do
diff --git a/test/post_spec.rb b/test/post_spec.rb
index 43f8c85..f868198 100644
--- a/test/post_spec.rb
+++ b/test/post_spec.rb
@@ -9,6 +9,21 @@
     @posts = subject.posts
   end
 
+  around :each do |example|
+    begin
+      d = Serif::Draft.new(subject)
+      d.slug = "foo-bar-bar-temp"
+      d.title = "Testing title"
+      d.save("# some content")
+      d.publish!
+      @temporary_post = Serif::Post.from_slug(subject, d.slug)
+
+      example.run
+    ensure
+      FileUtils.rm(@temporary_post.path)
+    end
+  end
+
   it "uses the config file's permalink value" do
     @posts.all? { |p| p.url == "/test-blog/#{p.slug}" }.should be_true
   end
@@ -18,4 +33,78 @@
       @posts.all? { |p| p.inspect.should include(p.headers.inspect) }
     end
   end
+
+  describe "#autoupdate=" do
+    it "sets the 'update' header to 'now' if truthy assigned value" do
+      @temporary_post.autoupdate = true
+      @temporary_post.headers[:update].should == "now"
+    end
+
+    it "removes the 'update' header entirely if falsey assigned value" do
+      @temporary_post.autoupdate = false
+      @temporary_post.headers.key?(:update).should be_false
+    end
+
+    it "marks the post as autoupdate? == true" do
+      @temporary_post.autoupdate?.should be_false
+      @temporary_post.autoupdate = true
+      @temporary_post.autoupdate?.should be_true
+    end
+  end
+
+  describe "#autoupdate?" do
+    it "returns true if there is an update: now header" do
+      @temporary_post.stub(:headers) { { :update => "foo" } }
+      @temporary_post.autoupdate?.should be_false
+      @temporary_post.stub(:headers) { { :update => "now" } }
+      @temporary_post.autoupdate?.should be_true
+    end
+
+    it "is ignorant of whitespace in the update header value" do
+      @temporary_post.stub(:headers) { { :update => "now" } }
+      @temporary_post.autoupdate?.should be_true
+
+      (1..3).each do |left|
+        (1..3).each do |right|
+          @temporary_post.stub(:headers) { { :update => "#{" " * left}now#{" " * right}"} }
+          @temporary_post.autoupdate?.should be_true
+        end
+      end
+    end
+  end
+
+  describe "#update!" do
+    it "sets the updated header timestamp to the current time" do
+      old_update_time = @temporary_post.updated
+      t = Time.now + 50
+
+      Timecop.freeze(t) do
+        @temporary_post.update!
+        @temporary_post.updated.should_not == old_update_time
+        @temporary_post.updated.to_i.should == t.to_i
+        @temporary_post.headers[:updated].to_i.should == t.to_i
+      end
+    end
+
+    it "calls save and writes out the new timestamp value, without a publish: now header" do
+      @temporary_post.should_receive(:save).once.and_call_original
+
+      t = Time.now + 50
+      Timecop.freeze(t) do
+        @temporary_post.update!
+
+        file_content = Redhead::String[File.read(@temporary_post.path)]
+        Time.parse(file_content.headers[:updated].value).to_i.should == t.to_i
+        file_content.headers[:publish].should be_nil
+      end
+    end
+
+    it "marks the post as no longer auto-updating" do
+      @temporary_post.autoupdate?.should be_false
+      @temporary_post.autoupdate = true
+      @temporary_post.autoupdate?.should be_true
+      @temporary_post.update!
+      @temporary_post.autoupdate?.should be_false
+    end
+  end
 end
\ No newline at end of file
diff --git a/test/site_generation_spec.rb b/test/site_generation_spec.rb
index a242401..57e496a 100644
--- a/test/site_generation_spec.rb
+++ b/test/site_generation_spec.rb
@@ -98,6 +98,34 @@
       Dir[File.join(testing_dir("_site/drafts/sample-draft"), "*.html")].size.should == 1
     end
 
+    context "for posts with an update: now header" do
+      around :each do |example|
+        begin
+          d = Serif::Draft.new(subject)
+          d.slug = "post-to-be-auto-updated"
+          d.title = "Testing title"
+          d.save("# some content")
+          d.publish!
+          
+          @temporary_post = Serif::Post.from_slug(subject, d.slug)
+          @temporary_post.autoupdate = true
+          @temporary_post.save
+
+          example.run
+        ensure
+          FileUtils.rm(@temporary_post.path)
+        end
+      end
+
+      it "sets the updated header to the current time" do
+        t = Time.now + 30
+        Timecop.freeze(t) do
+          capture_stdout { subject.generate }
+          Serif::Post.from_slug(subject, @temporary_post.slug).updated.to_i.should == t.to_i
+        end
+      end
+    end
+
     context "for drafts with a publish: now header" do
       before :all do
         @time = Time.utc(2012, 12, 21, 15, 30, 00)