diff --git a/Network/Gravatar.hs b/Network/Gravatar.hs
--- a/Network/Gravatar.hs
+++ b/Network/Gravatar.hs
@@ -10,29 +10,61 @@
 --
 --------------------------------------------------------------------
 --
--- Return the url of a gravatar
+-- Return the URL of a gravatar image - an image associated with an
+-- email address.
 --
 
 module Network.Gravatar (
-    gravatar
-    , Rating(..)
+    gravatar, gravatarWith
+    ,Rating(..)
+    ,Size,size
   ) where
 
 import Data.Digest.OpenSSL.MD5
 import Data.List
 import Data.Char
+import Network.URI
 import qualified Data.ByteString.Char8 as S
 
+------------------------------------------------------------------------
+-- Implementing the gravatar protocol
+
 -- | Classification ratings for gravatars
 data Rating = G | PG | R | X
     deriving (Eq,Ord,Bounded,Enum,Show,Read)
 
+-- | An image size in pixels from 1 to 80.
+newtype Size = Size Int
+
+-- | A smart constructor for the Size type, ensuring it is between 1 and 80
+size :: Int -> Maybe Size
+size n | n >= 1 && n <= 80 = Just (Size n)
+       | otherwise         = Nothing
+
+------------------------------------------------------------------------
+
 baseURL     = "http://www.gravatar.com/avatar.php?"
 gravatar_id = "gravatar_id"
 
--- | Return the url of a gravatar for an email address (a globally recognized avatar).
+-- | Return the url of a gravatar for an
+-- email address (a globally recognized avatar).
+--
 gravatar :: String -> String
-gravatar who = concat [baseURL ,gravatar_id ,"=" ,(md5sum (S.pack (clean who)))]
+gravatar who = gravatarWith who Nothing Nothing Nothing
+
+-- | Construct the url of a gravatar with optional classification
+-- ratings, an optional size, and optional default image.
+--
+gravatarWith :: String
+             -> Maybe Rating
+             -> Maybe Size
+             -> Maybe String
+             -> String
+gravatarWith who rating' sz' dflt'
+             = concat [baseURL ,gravatar_id ,"=" ,(md5sum (S.pack (clean who))),rating,sz,dflt ]
     where
-        clean = let f = reverse . dropWhile isSpace in f . f
+        clean  = let f = reverse . dropWhile isSpace in f . f
+        rating = maybe "" (\r        -> "&rating="++show r) rating'
+        sz     = maybe "" (\(Size n) -> "&size="++show n) sz'
+        dflt   = maybe "" (\r        -> "&default="++escapeURIString isUnreserved  r) dflt'
 
diff --git a/gravatar.cabal b/gravatar.cabal
--- a/gravatar.cabal
+++ b/gravatar.cabal
@@ -1,9 +1,9 @@
 name:                gravatar
-version:             0.1
+version:             0.2
 homepage:            http://code.haskell.org/~dons/code/gravatar
 synopsis:            Find the url of the gravatar associated with an email address.
 description:         
-    Gravatars <gravatar.com> are globally unique images associated with an email
+    Gravatars (<http://gravatar.com>) are globally unique images associated with an email
     address, widely used in social networking sites. This library
     lets you find the URL of a gravatar .png associated with an email
     address.
@@ -25,4 +25,4 @@
         build-depends: base >= 3, bytestring
     else
         build-depends: base < 3
-    build-depends: nano-md5
+    build-depends: nano-md5, network
diff --git a/tests/tests.hs b/tests/tests.hs
--- a/tests/tests.hs
+++ b/tests/tests.hs
@@ -2,3 +2,6 @@
 
 main = do
     print $ gravatar "dons@galois.com" == "http://www.gravatar.com/avatar.php?gravatar_id=f21827076a1d0725c4f4bd5a640102e9"
+
+    print $ (gravatarWith "dons@galois.com" (Just R) Nothing (Just "http://haskell.org") ) == "http://www.gravatar.com/avatar.php?gravatar_id=f21827076a1d0725c4f4bd5a640102e9&rating=R&default=http%3A%2F%2Fhaskell.org"
+