diff --git a/lib/microformats2/collection.rb b/lib/microformats2/collection.rb
index 475031c..8469ecc 100644
--- a/lib/microformats2/collection.rb
+++ b/lib/microformats2/collection.rb
@@ -25,7 +25,7 @@ module Microformats2
     end
 
     def all
-      @all ||= FormatParser.parse(@element).each do |format|
+      @all ||= FormatParser.parse(@element, @base).each do |format|
         save_format_name(format.method_name)
         define_method(format.method_name)
         set_value(format.method_name, format)
diff --git a/lib/microformats2/format.rb b/lib/microformats2/format.rb
index 0cd352f..7b642dc 100644
--- a/lib/microformats2/format.rb
+++ b/lib/microformats2/format.rb
@@ -4,8 +4,9 @@ module Microformats2
 
     attr_reader :method_name
 
-    def initialize(element)
+    def initialize(element, base)
       @element = element
+      @base = base
       @method_name = to_method_name(format_types.first)
       @property_names = []
     end
@@ -27,13 +28,13 @@ module Microformats2
     end
 
     def parse_properties
-      PropertyParser.parse(@element.children).each do |property|
+      PropertyParser.parse(@element.children, @base).each do |property|
         assign_property(property)
       end
     end
 
     def add_property(property_class, value)
-      property = Property.new(nil, property_class, value)
+      property = Property.new(nil, property_class, value, @base)
       assign_property(property)
     end
 
diff --git a/lib/microformats2/format_parser.rb b/lib/microformats2/format_parser.rb
index 0edcb0b..bee2a3e 100644
--- a/lib/microformats2/format_parser.rb
+++ b/lib/microformats2/format_parser.rb
@@ -1,7 +1,8 @@
 module Microformats2
   class FormatParser
     class << self
-      def parse(element)
+      def parse(element, base=nil)
+        @@base = base
         parse_node(element).flatten.compact
       end
 
@@ -31,7 +32,7 @@ module Microformats2
         const_name = constant_name(html_class)
         klass = find_or_create_ruby_class(const_name)
 
-        klass.new(element).parse
+        klass.new(element, @@base).parse
       end
 
       def format_classes(element)
diff --git a/lib/microformats2/property.rb b/lib/microformats2/property.rb
index 44eb9ab..3d35dd9 100644
--- a/lib/microformats2/property.rb
+++ b/lib/microformats2/property.rb
@@ -8,13 +8,13 @@ module Microformats2
       "e" => Embedded }
 
     class << self
-	    def new(element, property_class, value=nil)
+	    def new(element, property_class, value=nil, base=nil)
 	      # p-class-name -> p
 	      prefix = property_class.split("-").first
 	      # find ruby class for kind of property
 	      klass = PREFIX_CLASS_MAP[prefix]
 	      raise InvalidPropertyPrefix unless klass
-	      klass.new(element, property_class, value)
+	      klass.new(element, property_class, value, base)
 	    end
 	  end
   end
diff --git a/lib/microformats2/property/foundation.rb b/lib/microformats2/property/foundation.rb
index 75aa423..8851f8e 100644
--- a/lib/microformats2/property/foundation.rb
+++ b/lib/microformats2/property/foundation.rb
@@ -3,10 +3,11 @@ module Microformats2
     class Foundation
       attr_reader :method_name
 
-      def initialize(element, html_class, string_value=nil)
+      def initialize(element, html_class, string_value=nil, base=nil)
         @element = element
         @method_name = to_method_name(html_class)
         @string_value = string_value
+        @base = base
       end
 
       def parse
diff --git a/lib/microformats2/property/url.rb b/lib/microformats2/property/url.rb
index 1d45522..85847a6 100644
--- a/lib/microformats2/property/url.rb
+++ b/lib/microformats2/property/url.rb
@@ -2,6 +2,22 @@ module Microformats2
   module Property
     class Url < Foundation
 
+      def to_s
+        @to_s = absolutize(super.to_s)
+      end
+
+      # TODO: make dry, repeated in Collection
+      def absolutize(href)
+        uri = URI.parse(href)
+
+        if @base && !uri.absolute?
+          uri = URI.join(@base, href)
+        end
+
+        uri.normalize!
+        uri.to_s
+      end
+
       protected
 
       def attr_map
diff --git a/lib/microformats2/property_parser.rb b/lib/microformats2/property_parser.rb
index 62f00d1..003273d 100644
--- a/lib/microformats2/property_parser.rb
+++ b/lib/microformats2/property_parser.rb
@@ -1,7 +1,8 @@
 module Microformats2
   class PropertyParser
     class << self
-      def parse(element)
+      def parse(element, base)
+        @@base = base
         parse_node(element).flatten.compact
       end
 
@@ -26,8 +27,8 @@ module Microformats2
 
       def parse_property(element)
         property_classes(element).map do |property_class|
-          property   = Property.new(element, property_class).parse
-          properties = format_classes(element).empty? ? PropertyParser.parse(element.children) : []
+          property   = Property.new(element, property_class, nil, @@base).parse
+          properties = format_classes(element).empty? ? PropertyParser.parse(element.children, @@base) : []
 
           [property].concat properties
         end
diff --git a/spec/lib/microformats2/collection_spec.rb b/spec/lib/microformats2/collection_spec.rb
index 496f9c7..44e5c49 100644
--- a/spec/lib/microformats2/collection_spec.rb
+++ b/spec/lib/microformats2/collection_spec.rb
@@ -35,13 +35,13 @@ describe Microformats2::Collection do
           @collection.card.name.should be_kind_of Microformats2::Property::Text
         end
       end
-      describe "'.h-card .p-url'" do
+      describe "'.h-card .u-url'" do
         it "assigns all urls to HCard#urls" do
-          urls = ["http://flickr.com/jlsuttles", "http://twitter.com/jlsuttles"]
+          urls = ["http://example.org/", "http://flickr.com/", "http://twitter.com/jlsuttles"]
           @collection.card.urls.map(&:to_s).should == urls
         end
         it "assigns then first url to HCard#url" do
-          @collection.card.url.to_s.should == "http://flickr.com/jlsuttles"
+          @collection.card.url.to_s.should == "http://example.org/"
         end
         it "HCard#url is a Property::Url" do
           @collection.card.url.should be_kind_of Microformats2::Property::Url
@@ -176,7 +176,7 @@ describe Microformats2::Collection do
         end
       end
     end
-    
+
     describe "rels.html" do
       before do
         html = "spec/support/lib/microformats2/rels.html"
diff --git a/spec/support/lib/microformats2/simple.html b/spec/support/lib/microformats2/simple.html
index 42c60bd..551e9a2 100644
--- a/spec/support/lib/microformats2/simple.html
+++ b/spec/support/lib/microformats2/simple.html
@@ -1,10 +1,14 @@
 <!DOCTYPE html>
 <html>
+<base href="http://example.org/">
 <body>
   <div class="h-card">
-    <a href="http://flickr.com/jlsuttles" class="u-url p-name">
+    <a href="/" class="u-url p-name">
       Jessica Lynn Suttles
     </a>
+    <a href="http://flickr.com" class="u-url">
+      @jlsuttles
+    </a>
     <a href="http://twitter.com/jlsuttles" class="u-url">
       @jlsuttles
     </a>
diff --git a/spec/support/lib/microformats2/simple.js b/spec/support/lib/microformats2/simple.js
index c549abf..e36fe70 100644
--- a/spec/support/lib/microformats2/simple.js
+++ b/spec/support/lib/microformats2/simple.js
@@ -1,7 +1,7 @@
 { "items": [{
     "type": ["h-card"],
     "properties": {
-      "url": ["http://flickr.com/jlsuttles", "http://twitter.com/jlsuttles"],
+      "url": ["http://example.org/", "http://flickr.com/", "http://twitter.com/jlsuttles"],
       "name": ["Jessica Lynn Suttles"],
       "bday": ["1990-10-15"],
       "content": ["<p>Vegan. Cat lover. Coder.</p>"]