diff --git a/hakyll.cabal b/hakyll.cabal
index 165611f..00d618f 100644
--- a/hakyll.cabal
+++ b/hakyll.cabal
@@ -120,7 +120,7 @@ Library
     Hakyll.Web.Pandoc
     Hakyll.Web.Pandoc.Biblio
     Hakyll.Web.Pandoc.FileType
-    -- Hakyll.Web.Tags
+    Hakyll.Web.Tags
     Hakyll.Web.Template
     Hakyll.Web.Template.Context
     Hakyll.Web.Template.List
diff --git a/src/Hakyll/Core/Identifier/Pattern.hs b/src/Hakyll/Core/Identifier/Pattern.hs
index 48e5441..eb9da374 100644
--- a/src/Hakyll/Core/Identifier/Pattern.hs
+++ b/src/Hakyll/Core/Identifier/Pattern.hs
@@ -68,6 +68,8 @@ import           Data.Binary            (Binary (..), getWord8, putWord8)
 import           Data.List              (inits, isPrefixOf, tails)
 import           Data.Maybe             (isJust)
 import           Data.Monoid            (Monoid, mappend, mempty)
+import           Data.Set               (Set)
+import qualified Data.Set               as S
 
 
 --------------------------------------------------------------------------------
@@ -108,7 +110,7 @@ data Pattern
     | Complement Pattern
     | And Pattern Pattern
     | Glob [GlobComponent]
-    | List [Identifier]  -- TODO Maybe use a set here
+    | List (Set Identifier)
     | Regex String
     | Version (Maybe String)
     deriving (Show)
@@ -162,7 +164,7 @@ fromGlob = Glob . parse'
 --------------------------------------------------------------------------------
 -- | Create a 'Pattern' from a list of 'Identifier's it should match
 fromList :: [Identifier] -> Pattern
-fromList = List
+fromList = List . S.fromList
 
 
 --------------------------------------------------------------------------------
@@ -205,7 +207,7 @@ matches Everything     _ = True
 matches (Complement p) i = not $ matches p i
 matches (And x y)      i = matches x i && matches y i
 matches (Glob p)       i = isJust $ capture (Glob p) i
-matches (List l)       i = i `elem` l
+matches (List l)       i = i `S.member` l
 matches (Regex r)      i = toFilePath i =~ r
 matches (Version v)    i = identifierVersion i == v
 
diff --git a/src/Hakyll/Web/Tags.hs b/src/Hakyll/Web/Tags.hs
index e10af56..2aa1cac 100644
--- a/src/Hakyll/Web/Tags.hs
+++ b/src/Hakyll/Web/Tags.hs
@@ -66,6 +66,7 @@ import qualified Text.Blaze.Html5.Attributes     as A
 --------------------------------------------------------------------------------
 import           Hakyll.Core.Compiler
 import           Hakyll.Core.Identifier
+import           Hakyll.Core.Identifier.Pattern
 import           Hakyll.Core.Item
 import           Hakyll.Core.Metadata
 import           Hakyll.Core.Util.String
@@ -102,10 +103,11 @@ getCategory = return . return . takeBaseName . takeDirectory . toFilePath
 
 
 --------------------------------------------------------------------------------
--- | Higher-level function to read tags
+-- | Higher-order function to read tags
 buildTagsWith :: MonadMetadata m
-              => (Identifier -> m [String]) -> [Identifier] -> m Tags
-buildTagsWith f ids = do
+              => (Identifier -> m [String]) -> Pattern -> m Tags
+buildTagsWith f pattern = do
+    ids    <- getMatches pattern
     tagMap <- foldM addTags M.empty ids
     return $ Tags $ M.toList tagMap
   where
@@ -117,15 +119,13 @@ buildTagsWith f ids = do
 
 --------------------------------------------------------------------------------
 -- | Read a tagmap using the @tags@ metadata field
--- TODO: Should use pattern
-buildTags :: MonadMetadata m => [Identifier] -> m Tags
+buildTags :: MonadMetadata m => Pattern -> m Tags
 buildTags = buildTagsWith getTags
 
 
 --------------------------------------------------------------------------------
 -- | Read a tagmap using the @category@ metadata field
--- TODO: Should use pattern
-buildCategory :: MonadMetadata m => [Identifier] -> m Tags
+buildCategory :: MonadMetadata m => Pattern -> m Tags
 buildCategory = buildTagsWith getCategory
 
 
diff --git a/src/Hakyll/Web/Template/Context.hs b/src/Hakyll/Web/Template/Context.hs
index 3b98ea3..67c4070 100644
--- a/src/Hakyll/Web/Template/Context.hs
+++ b/src/Hakyll/Web/Template/Context.hs
@@ -28,8 +28,7 @@ import qualified Data.Map                      as M
 import           Data.Monoid                   (Monoid (..))
 import           Data.Time.Clock               (UTCTime (..))
 import           Data.Time.Format              (formatTime, parseTime)
-import           System.FilePath               (takeBaseName, takeDirectory,
-                                                takeFileName)
+import           System.FilePath               (takeBaseName, takeFileName)
 import           System.Locale                 (TimeLocale, defaultTimeLocale)