diff --git a/ChangeLog.md b/ChangeLog.md
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+++ b/ChangeLog.md
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+# Revision history for commutative-semigroups
+
+## Unreleased
+
+Initial version, created from `groups` package.
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+Copyright (c) 2013, Nathan "Taneb" van Doorn
+              2021, Obsidian Systems LLC
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Nathan "Taneb" van Doorn nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/ReadMe.md b/ReadMe.md
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+++ b/ReadMe.md
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+# Commutative Semigroup
+
+[![Haskell](https://img.shields.io/badge/language-Haskell-orange.svg)](https://haskell.org) [![Hackage](https://img.shields.io/hackage/v/commutative-semigroup.svg)](https://hackage.haskell.org/package/commutative-semigroup) [![Hackage CI](https://matrix.hackage.haskell.org/api/v2/packages/commutative-semigroup/badge)](https://matrix.hackage.haskell.org/#/package/commutative-semigroup)  [![BSD3 License](https://img.shields.io/badge/license-BSD3-blue.svg)](https://github.com/reflex-frp/commutative-semigroup/LICENSE)
+
+A commutative semigroup is a semigroup where the order of arguments to mappend does not matter.
+
+```haskell
+class Semigroup g => Commutative g
+```
diff --git a/Setup.hs b/Setup.hs
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+++ b/Setup.hs
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+import Distribution.Simple
+main = defaultMain
diff --git a/commutative-semigroups.cabal b/commutative-semigroups.cabal
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+++ b/commutative-semigroups.cabal
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+cabal-version:       2.4
+name:                commutative-semigroups
+version:             0.0.0.0
+synopsis:            Commutative semigroups
+description:
+  A commutative semigroup is a semigroup where the order of arguments to mappend does not matter.
+license:             BSD-3-Clause
+license-file:        LICENSE
+author:              Nathan "Taneb" van Doorn
+maintainer:          mainainer@obsidian.systems
+copyright:           Copyright (C) 2013 Nathan van Doorn, 2021 Obsidian Systems LLC
+category:            Algebra, Data, Math
+build-type:          Simple
+bug-reports:         https://github.com/ObsidianSystems/commutative-semigroups/issues
+extra-source-files:
+  ChangeLog.md
+  ReadMe.md
+
+source-repository head
+  type:     git
+  location: https://github.com/ObsidianSystems/commutative-semigroups.git
+
+library
+  exposed-modules:     Data.Semigroup.Commutative
+  -- other-modules:
+  build-depends:       base >= 4.6 && < 5
+  hs-source-dirs:      src
+  default-language:    Haskell2010
diff --git a/src/Data/Semigroup/Commutative.hs b/src/Data/Semigroup/Commutative.hs
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--- /dev/null
+++ b/src/Data/Semigroup/Commutative.hs
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+{-# LANGUAGE CPP           #-}
+#if MIN_VERSION_base(4,12,0)
+{-# LANGUAGE TypeOperators #-}
+#endif
+
+module Data.Semigroup.Commutative where
+
+import Data.Monoid
+import Data.Ord
+import Data.List (unfoldr)
+#if MIN_VERSION_base(4,7,0)
+import Data.Proxy
+#endif
+#if MIN_VERSION_base(4,9,0) && !MIN_VERSION_base(4,11,0)
+import Data.Semigroup (Semigroup(..))
+#endif
+#if MIN_VERSION_base(4,9,0)
+import Data.Functor.Const
+import Data.Functor.Identity
+#endif
+#if MIN_VERSION_base(4,12,0)
+import Data.Functor.Contravariant (Op(Op))
+import GHC.Generics
+#endif
+
+-- |An 'Commutative' semigroup is a 'Semigroup' that follows the rule:
+--
+-- @a \<> b == b \<> a@
+class
+#if MIN_VERSION_base(4,9,0)
+     Semigroup g
+#else
+     Monoid g
+#endif
+  => Commutative g
+
+-- | Trivial commutative semigroup.
+instance Commutative ()
+
+instance Num a => Commutative (Sum a)
+
+instance Fractional a => Commutative (Product a)
+
+instance Commutative a => Commutative (Dual a)
+
+-- | Functions lift commutative semigroups pointwise.
+instance Commutative b => Commutative (a -> b)
+
+-- | Product commutative semigroup.
+-- A Pair of commutative semigroups gives rise to a commutative semigroup
+instance (Commutative a, Commutative b) => Commutative (a, b)
+
+instance (Commutative a, Commutative b, Commutative c) => Commutative (a, b, c)
+
+instance (Commutative a, Commutative b, Commutative c, Commutative d) => Commutative (a, b, c, d)
+
+instance (Commutative a, Commutative b, Commutative c, Commutative d, Commutative e) => Commutative (a, b, c, d, e)
+
+#if MIN_VERSION_base(4,11,0)
+instance Commutative a => Commutative (Down a)
+#endif
+
+#if MIN_VERSION_base(4,7,0)
+-- | Trivial commutative semigroup, Functor style.
+instance Commutative (Proxy x)
+#endif
+
+-- 'Const' has existed for a long time, but the Monoid instance
+-- arrives in base-4.9.0.0. Similarly, 'Identity' was defined in
+-- base-4.8.0.0 but doesn't get the Monoid instance until base-4.9.0.0
+#if MIN_VERSION_base(4,9,0)
+-- | 'Const' lifts commutative semigroups into a functor.
+instance Commutative a => Commutative (Const a x)
+
+-- | 'Identity' lifts commutative semigroups pointwise (at only one point).
+instance Commutative a => Commutative (Identity a)
+#endif
+
+-- (:*:) and (:.:) exist since base-4.6.0.0 but the Monoid instances
+-- arrive in base-4.12.0.0.
+-- Also, contravariant was moved into base in this version.
+#if MIN_VERSION_base(4,12,0)
+-- | Product of commutative semigroups, Functor style.
+instance (Commutative (f a), Commutative (g a)) => Commutative ((f :*: g) a)
+
+-- See https://gitlab.haskell.org/ghc/ghc/issues/11135#note_111802 for the reason Compose is not also provided.
+-- Base does not define Monoid (Compose f g a) so this is the best we can
+-- really do for functor composition.
+instance Commutative (f (g a)) => Commutative ((f :.: g) a)
+
+instance Commutative a => Commutative (Op a b)
+#endif