diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,4 +1,7 @@
-0.5.10
+0.5.11:
+	* Add replaceExtension and fileExtension
+
+0.5.10:
 	* Disallow /. for absolute file
 	* Disallow foo/. for relative file
 
diff --git a/path.cabal b/path.cabal
--- a/path.cabal
+++ b/path.cabal
@@ -1,5 +1,5 @@
 name:                path
-version:             0.5.10
+version:             0.5.11
 synopsis:            Support for well-typed paths
 description:         Support for well-typed paths.
 license:             BSD3
diff --git a/src/Path.hs b/src/Path.hs
--- a/src/Path.hs
+++ b/src/Path.hs
@@ -41,6 +41,8 @@
   ,parent
   ,filename
   ,dirname
+  ,fileExtension
+  ,setFileExtension
   -- * Conversion
   ,toFilePath
   ,fromAbsDir
@@ -54,6 +56,7 @@
 import           Control.Monad.Catch (MonadThrow(..))
 import           Data.Aeson (FromJSON (..))
 import qualified Data.Aeson.Types as Aeson
+import           Data.Coerce
 import           Data.Data
 import           Data.List
 import           Data.Maybe
@@ -149,7 +152,8 @@
   if not (FilePath.isAbsolute filepath) &&
      not (hasParentDir filepath) &&
      not (null filepath) &&
-     filepath /= "." && (normalizeFilePath filepath) /= curDirNormalizedFP &&
+     filepath /= "." &&
+     normalizeFilePath filepath /= curDirNormalizedFP &&
      filepath /= ".." &&
      FilePath.isValid filepath
      then return (Path (normalizeDir filepath))
@@ -391,6 +395,25 @@
 dirname :: Path b Dir -> Path Rel Dir
 dirname (Path l) =
   Path (last (FilePath.splitPath l))
+
+-- | Get extension from given file path.
+--
+-- @since 0.5.11
+fileExtension :: Path b File -> String
+fileExtension = FilePath.takeExtension . toFilePath
+
+-- | Replace\/add extension to given file path. Throws if the
+-- resulting filename does not parse.
+--
+-- @since 0.5.11
+setFileExtension :: MonadThrow m
+  => String            -- ^ Extension to set
+  -> Path b File       -- ^ Old file name
+  -> m (Path b File)   -- ^ New file name with the desired extension
+setFileExtension ext (Path path) =
+  if FilePath.isAbsolute path
+    then fmap coerce (parseAbsFile (FilePath.replaceExtension path ext))
+    else fmap coerce (parseRelFile (FilePath.replaceExtension path ext))
 
 --------------------------------------------------------------------------------
 -- Internal functions