diff --git a/fasta.cabal b/fasta.cabal
--- a/fasta.cabal
+++ b/fasta.cabal
@@ -10,7 +10,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.10.3.0
+version:             0.10.4.0
 
 -- A short (one-line) description of the package.
 synopsis:            A simple, mindless parser for fasta files.
@@ -48,6 +48,7 @@
 library
   -- Modules exported by the library.
   exposed-modules:    Data.Fasta.Category,
+                      Data.Fasta.Utility,
                       Data.Fasta.String,
                       Data.Fasta.String.Types,
                       Data.Fasta.String.Parse,
diff --git a/src/Data/Fasta/ByteString/Lazy/Utility.hs b/src/Data/Fasta/ByteString/Lazy/Utility.hs
--- a/src/Data/Fasta/ByteString/Lazy/Utility.hs
+++ b/src/Data/Fasta/ByteString/Lazy/Utility.hs
@@ -5,6 +5,8 @@
 -}
 
 module Data.Fasta.ByteString.Lazy.Utility ( getField
+                                          , compl
+                                          , revCompl
                                           ) where
 
 -- Built in
@@ -14,8 +16,17 @@
 
 -- Local
 import Data.Fasta.ByteString.Lazy.Types
+import Data.Fasta.Utility
 
 -- | Gets a 1 indexed field from the header of a fasta sequence using a certain
 -- delimiter.
 getField :: Int -> Char -> FastaSequence -> BL.ByteString
 getField field delim = (!! (field - 1)) . BL.split delim . fastaHeader
+
+-- | Gets the complement of the sequence.
+compl :: FastaSequence -> FastaSequence
+compl fs = fs { fastaSeq = BL.map complRules . fastaSeq $ fs }
+
+-- | Gets the reverse complement of the sequence.
+revCompl :: FastaSequence -> FastaSequence
+revCompl fs = fs { fastaSeq = BL.reverse . BL.map complRules . fastaSeq $ fs }
diff --git a/src/Data/Fasta/ByteString/Utility.hs b/src/Data/Fasta/ByteString/Utility.hs
--- a/src/Data/Fasta/ByteString/Utility.hs
+++ b/src/Data/Fasta/ByteString/Utility.hs
@@ -5,6 +5,8 @@
 -}
 
 module Data.Fasta.ByteString.Utility ( getField
+                                     , compl
+                                     , revCompl
                                      ) where
 
 -- Built in
@@ -14,8 +16,17 @@
 
 -- Local
 import Data.Fasta.ByteString.Types
+import Data.Fasta.Utility
 
 -- | Gets a 1 indexed field from the header of a fasta sequence using a certain
 -- delimiter.
 getField :: Int -> Char -> FastaSequence -> B.ByteString
 getField field delim = (!! (field - 1)) . B.split delim . fastaHeader
+
+-- | Gets the complement of the sequence.
+compl :: FastaSequence -> FastaSequence
+compl fs = fs { fastaSeq = B.map complRules . fastaSeq $ fs }
+
+-- | Gets the reverse complement of the sequence.
+revCompl :: FastaSequence -> FastaSequence
+revCompl fs = fs { fastaSeq = B.reverse . B.map complRules . fastaSeq $ fs }
diff --git a/src/Data/Fasta/String/Utility.hs b/src/Data/Fasta/String/Utility.hs
--- a/src/Data/Fasta/String/Utility.hs
+++ b/src/Data/Fasta/String/Utility.hs
@@ -5,6 +5,8 @@
 -}
 
 module Data.Fasta.String.Utility ( getField
+                                 , compl
+                                 , revCompl
                                  ) where
 
 -- Built in
@@ -14,8 +16,17 @@
 
 -- Local
 import Data.Fasta.String.Types
+import Data.Fasta.Utility
 
 -- | Gets a 1 indexed field from the header of a fasta sequence using a certain
 -- delimiter.
 getField :: Int -> Char -> FastaSequence -> String
 getField field delim = (!! (field - 1)) . Split.splitWhen (== delim) . fastaHeader
+
+-- | Gets the complement of the sequence.
+compl :: FastaSequence -> FastaSequence
+compl fs = fs { fastaSeq = fmap complRules . fastaSeq $ fs }
+
+-- | Gets the reverse complement of the sequence.
+revCompl :: FastaSequence -> FastaSequence
+revCompl fs = fs { fastaSeq = reverse . fmap complRules . fastaSeq $ fs }
diff --git a/src/Data/Fasta/Text/Lazy/Utility.hs b/src/Data/Fasta/Text/Lazy/Utility.hs
--- a/src/Data/Fasta/Text/Lazy/Utility.hs
+++ b/src/Data/Fasta/Text/Lazy/Utility.hs
@@ -5,6 +5,8 @@
 -}
 
 module Data.Fasta.Text.Lazy.Utility ( getField
+                                    , compl
+                                    , revCompl
                                     ) where
 
 -- Built in
@@ -14,8 +16,17 @@
 
 -- Local
 import Data.Fasta.Text.Lazy.Types
+import Data.Fasta.Utility
 
 -- | Gets a 1 indexed field from the header of a fasta sequence using a certain
 -- delimiter.
 getField :: Int -> Char -> FastaSequence -> T.Text
 getField field delim = (!! (field - 1)) . T.split (== delim) . fastaHeader
+
+-- | Gets the complement of the sequence.
+compl :: FastaSequence -> FastaSequence
+compl fs = fs { fastaSeq = T.map complRules . fastaSeq $ fs }
+
+-- | Gets the reverse complement of the sequence.
+revCompl :: FastaSequence -> FastaSequence
+revCompl fs = fs { fastaSeq = T.reverse . T.map complRules . fastaSeq $ fs }
diff --git a/src/Data/Fasta/Text/Utility.hs b/src/Data/Fasta/Text/Utility.hs
--- a/src/Data/Fasta/Text/Utility.hs
+++ b/src/Data/Fasta/Text/Utility.hs
@@ -5,6 +5,8 @@
 -}
 
 module Data.Fasta.Text.Utility ( getField
+                               , compl
+                               , revCompl
                                ) where
 
 -- Built in
@@ -14,8 +16,17 @@
 
 -- Local
 import Data.Fasta.Text.Types
+import Data.Fasta.Utility
 
 -- | Gets a 1 indexed field from the header of a fasta sequence using a certain
 -- delimiter.
 getField :: Int -> Char -> FastaSequence -> T.Text
 getField field delim = (!! (field - 1)) . T.split (== delim) . fastaHeader
+
+-- | Gets the complement of the sequence.
+compl :: FastaSequence -> FastaSequence
+compl fs = fs { fastaSeq = T.map complRules . fastaSeq $ fs }
+
+-- | Gets the reverse complement of the sequence.
+revCompl :: FastaSequence -> FastaSequence
+revCompl fs = fs { fastaSeq = T.reverse . T.map complRules . fastaSeq $ fs }
diff --git a/src/Data/Fasta/Utility.hs b/src/Data/Fasta/Utility.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Fasta/Utility.hs
@@ -0,0 +1,27 @@
+-- Utility Module
+-- By Gregory W. Schwartz
+
+{- | Collects all helpful random functions.
+-}
+
+module Data.Fasta.Utility ( complRules
+                          ) where
+
+-- Built in
+
+-- Cabal
+
+-- Local
+
+-- | Defines the rules for complement. Unknown characters are left
+-- untouched.
+complRules :: Char -> Char
+complRules 'A' = 'T'
+complRules 'C' = 'G'
+complRules 'G' = 'C'
+complRules 'T' = 'A'
+complRules 'a' = 't'
+complRules 'c' = 'g'
+complRules 'g' = 'c'
+complRules 't' = 'a'
+complRules x   = x