diff --git a/Data/Map/Class.hs b/Data/Map/Class.hs
--- a/Data/Map/Class.hs
+++ b/Data/Map/Class.hs
@@ -18,11 +18,6 @@
 import Util ((∘), (∘∘), compose2, bind2)
 import Util.Private (Endo (..))
 
--- | Laws:
---
--- * @'adjustA' 'pure' _ = 'pure'@
---
--- * @'adjustA' 'Const' k '<=<' 'traverseWithKey' f = 'fmap' 'Const' '.' f k '<=<' 'getConst' '.' 'adjustA' 'Const' k@
 class Traversable map => StaticMap map where
     type Key map
     adjustA :: Applicative p => (a -> p a) -> Key map -> map a -> p (map a)
@@ -228,8 +223,26 @@
 mapKeys :: (StaticMap m, Map n) => (Key m -> Key n) -> m a -> n a
 mapKeys f = foldrWithKey (insert . f) empty
 
+mapKeysWith :: (StaticMap m, Map n) => (a -> a -> a) -> (Key m -> Key n) -> m a -> n a
+mapKeysWith combine f = foldrWithKey (insertWith combine . f) empty
+
 traverseKeys :: (StaticMap m, Map n, Applicative p) => (Key m -> p (Key n)) -> m a -> p (n a)
 traverseKeys f = fmap (flip appEndo empty) . foldMapWithKeyA (\ i a -> (\ j -> Endo $ insert j a) <$> f i)
+
+traverseKeysWith :: (StaticMap m, Map n, Applicative p) => (a -> a -> a) -> (Key m -> p (Key n)) -> m a -> p (n a)
+traverseKeysWith combine f = fmap (flip appEndo empty) . foldMapWithKeyA (\ i a -> (\ j -> Endo $ insertWith combine j a) <$> f i)
+
+mapKeysMaybe :: (StaticMap m, Map n) => (Key m -> Maybe (Key n)) -> m a -> n a
+mapKeysMaybe f = runIdentity . traverseKeysMaybe (Identity . f)
+
+mapKeysMaybeWith :: (StaticMap m, Map n) => (a -> a -> a) -> (Key m -> Maybe (Key n)) -> m a -> n a
+mapKeysMaybeWith combine f = runIdentity . traverseKeysMaybeWith combine (Identity . f)
+
+traverseKeysMaybe :: (StaticMap m, Map n, Applicative p) => (Key m -> p (Maybe (Key n))) -> m a -> p (n a)
+traverseKeysMaybe f = fmap (flip appEndo empty) . foldMapWithKeyA (\ i a -> foldMap (\ j -> Endo $ insert j a) <$> f i)
+
+traverseKeysMaybeWith :: (StaticMap m, Map n, Applicative p) => (a -> a -> a) -> (Key m -> p (Maybe (Key n))) -> m a -> p (n a)
+traverseKeysMaybeWith combine f = fmap (flip appEndo empty) . foldMapWithKeyA (\ i a -> foldMap (\ j -> Endo $ insertWith combine j a) <$> f i)
 
 keys :: StaticMap map => map a -> map (Key map)
 keys = mapWithKey pure
diff --git a/Map.cabal b/Map.cabal
--- a/Map.cabal
+++ b/Map.cabal
@@ -1,5 +1,5 @@
 name:                Map
-version:             0.1.2.0
+version:             0.1.3.0
 synopsis:            Class of key-value maps
 -- description:
 license:             BSD3