diff --git a/changelog.md b/changelog.md
index 1eec4fa..d0b74ad 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,6 +1,9 @@
 Unreleased (3.1.1)
 ========
 
+- @JoseD92
+  - [#149](https://github.com/bitemyapp/esqueleto/pull/149): Added `upsert` support.
+
 - @parsonsmatt
   - [#133](https://github.com/bitemyapp/esqueleto/pull/133): Added `renderQueryToText` and related functions.
 
diff --git a/src/Database/Esqueleto/Internal/Internal.hs b/src/Database/Esqueleto/Internal/Internal.hs
index c464807..d6d165b 100644
--- a/src/Database/Esqueleto/Internal/Internal.hs
+++ b/src/Database/Esqueleto/Internal/Internal.hs
@@ -1263,6 +1263,7 @@ data UnexpectedCaseError =
   | InsertionFinalError
   | NewIdentForError
   | UnsafeSqlCaseError
+  | OperationNotSupported
   deriving (Show)
 
 data SqlBinOpCompositeError =
diff --git a/src/Database/Esqueleto/PostgreSQL.hs b/src/Database/Esqueleto/PostgreSQL.hs
index b89cac7..cbbf788 100644
--- a/src/Database/Esqueleto/PostgreSQL.hs
+++ b/src/Database/Esqueleto/PostgreSQL.hs
@@ -18,6 +18,8 @@ module Database.Esqueleto.PostgreSQL
   , chr
   , now_
   , random_
+  , upsert
+  , upsertBy
   -- * Internal
   , unsafeSqlAggregateFunction
   ) where
@@ -28,8 +30,17 @@ import           Data.Semigroup
 import qualified Data.Text.Internal.Builder                   as TLB
 import           Data.Time.Clock                              (UTCTime)
 import           Database.Esqueleto.Internal.Language         hiding (random_)
-import           Database.Esqueleto.Internal.PersistentImport
+import           Database.Esqueleto.Internal.PersistentImport hiding (upsert, upsertBy)
 import           Database.Esqueleto.Internal.Sql
+import           Database.Esqueleto.Internal.Internal         (EsqueletoError(..), CompositeKeyError(..), 
+                                                              UnexpectedCaseError(..), SetClause)
+import           Database.Persist.Class                       (OnlyOneUniqueKey)
+import           Data.List.NonEmpty                           ( NonEmpty( (:|) ) )
+import           Control.Arrow                                ((***), first)
+import           Control.Exception                            (Exception, throw, throwIO)
+import           Control.Monad.IO.Class                       (MonadIO (..))
+import qualified Control.Monad.Trans.Reader                   as R
+
 
 -- | (@random()@) Split out into database specific modules
 -- because MySQL uses `rand()`.
@@ -152,3 +163,54 @@ chr = unsafeSqlFunction "chr"
 
 now_ :: SqlExpr (Value UTCTime)
 now_ = unsafeSqlValue "NOW()"
+
+upsert :: (MonadIO m,
+      PersistEntity record,
+      OnlyOneUniqueKey record,
+      PersistRecordBackend record SqlBackend,
+      IsPersistBackend (PersistEntityBackend record))
+    => record
+    -- ^ new record to insert
+    -> [SqlExpr (Update record)]
+    -- ^ updates to perform if the record already exists
+    -> R.ReaderT SqlBackend m (Entity record)
+    -- ^ the record in the database after the operation
+upsert record updates = do
+    uniqueKey <- onlyUnique record
+    upsertBy uniqueKey record updates
+
+upsertBy :: (MonadIO m,
+    PersistEntity record,
+    IsPersistBackend (PersistEntityBackend record))
+  => Unique record
+  -- ^ uniqueness constraint to find by
+  -> record
+  -- ^ new record to insert
+  -> [SqlExpr (Update record)]
+  -- ^ updates to perform if the record already exists
+  -> R.ReaderT SqlBackend m (Entity record)
+  -- ^ the record in the database after the operation
+upsertBy uniqueKey record updates = do
+  sqlB <- R.ask
+  maybe
+    (throw (UnexpectedCaseErr OperationNotSupported)) -- Postgres backend should have connUpsertSql, if this error is thrown, check changes on persistent 
+    (handler sqlB)
+    (connUpsertSql sqlB)
+  where
+    addVals l = map toPersistValue (toPersistFields record) ++ l ++ persistUniqueToValues uniqueKey
+    entDef = entityDef (Just record)
+    uDef = head $ filter ((==) (persistUniqueToFieldNames uniqueKey) . uniqueFields) $ entityUniques entDef
+    updatesText conn = first builderToText $ renderUpdates conn updates
+    handler conn f = fmap head $ uncurry rawSql $
+      (***) (f entDef (uDef :| [])) addVals $ updatesText conn
+    renderUpdates :: SqlBackend
+        -> [SqlExpr (Update val)]
+        -> (TLB.Builder, [PersistValue])
+    renderUpdates conn = uncommas' . concatMap renderUpdate
+        where
+          mk :: SqlExpr (Value ()) -> [(TLB.Builder, [PersistValue])]
+          mk (ERaw _ f)        = [f info]
+          mk (ECompositeKey _) = throw (CompositeKeyErr MakeSetError) -- FIXME
+          renderUpdate :: SqlExpr (Update val) -> [(TLB.Builder, [PersistValue])]
+          renderUpdate (ESet f) = mk (f undefined) -- second parameter of f is always unused
+          info = (projectBackend conn, initialIdentState)
\ No newline at end of file
diff --git a/test/Common/Test.hs b/test/Common/Test.hs
index a5450fb..9c6d367 100644
--- a/test/Common/Test.hs
+++ b/test/Common/Test.hs
@@ -25,11 +25,14 @@ module Common.Test
     , testAscRandom
     , testRandomMath
     , migrateAll
+    , migrateUnique
     , cleanDB
+    , cleanUniques
     , RunDbMonad
     , Run
     , p1, p2, p3, p4, p5
     , l1, l2, l3
+    , u1, u2, u3, u4
     , insert'
     , EntityField (..)
     , Foo (..)
@@ -48,6 +51,7 @@ module Common.Test
     , Point (..)
     , Circle (..)
     , Numbers (..)
+    , OneUnique(..)
     ) where
 
 import Control.Monad (forM_, replicateM, replicateM_, void)
@@ -157,8 +161,14 @@ share [mkPersist sqlSettings, mkMigrate "migrateAll"] [persistUpperCase|
     double Double
 |]
 
-
-
+-- Unique Test schema
+share [mkPersist sqlSettings, mkMigrate "migrateUnique"] [persistUpperCase|
+  OneUnique
+    name String
+    value Int
+    UniqueValue value
+    deriving Eq Show
+|]
 
 -- | this could be achieved with S.fromList, but not all lists
 --   have Ord instances
@@ -196,7 +206,17 @@ l2 = Lord "Dorset" Nothing
 l3 :: Lord
 l3 = Lord "Chester" (Just 17)
 
+u1 :: OneUnique
+u1 = OneUnique "First" 0
 
+u2 :: OneUnique
+u2 = OneUnique "Second" 1
+
+u3 :: OneUnique
+u3 = OneUnique "Third" 0
+
+u4 :: OneUnique
+u4 = OneUnique "First" 2
 
 testSelect :: Run -> Spec
 testSelect run = do
@@ -1536,3 +1556,10 @@ cleanDB = do
   delete $ from $ \(_ :: SqlExpr (Entity Point))      -> return ()
 
   delete $ from $ \(_ :: SqlExpr (Entity Numbers))    -> return ()
+
+
+cleanUniques
+  :: (forall m. RunDbMonad m
+  => SqlPersistT (R.ResourceT m) ())
+cleanUniques =
+  delete $ from $ \(_ :: SqlExpr (Entity OneUnique))    -> return ()
\ No newline at end of file
diff --git a/test/PostgreSQL/Test.hs b/test/PostgreSQL/Test.hs
index 8f2c4a2..407cb41 100644
--- a/test/PostgreSQL/Test.hs
+++ b/test/PostgreSQL/Test.hs
@@ -33,7 +33,7 @@ import qualified Database.Esqueleto.PostgreSQL as EP
 import Database.Esqueleto.PostgreSQL.JSON hiding ((?.), (-.), (||.))
 import qualified Database.Esqueleto.PostgreSQL.JSON as JSON
 import Database.Persist.Postgresql (withPostgresqlConn)
-import Database.PostgreSQL.Simple (SqlError(..))
+import Database.PostgreSQL.Simple (SqlError(..), ExecStatus(..))
 import System.Environment
 import Test.Hspec
 
@@ -949,6 +949,34 @@ testHashMinusOperator =
           where_ $ v @>. jsonbVal (object [])
           where_ $ f v
 
+testInsertUniqueViolation :: Spec
+testInsertUniqueViolation =
+  describe "Unique Violation on Insert" $
+    it "Unique throws exception" $ run (do
+      _ <- insert u1
+      _ <- insert u2
+      insert u3) `shouldThrow` (==) exception
+  where
+    exception = SqlError {
+      sqlState = "23505", 
+      sqlExecStatus = FatalError, 
+      sqlErrorMsg = "duplicate key value violates unique constraint \"UniqueValue\"", 
+      sqlErrorDetail = "Key (value)=(0) already exists.", 
+      sqlErrorHint = ""}
+
+testUpsert :: Spec
+testUpsert =
+  describe "Upsert test" $ do
+    it "Upsert can insert like normal" $ run $ do
+      u1e <- EP.upsert u1 [OneUniqueName =. val "fifth"]
+      liftIO $ entityVal u1e `shouldBe` u1
+    it "Upsert performs update on collision" $ run $ do
+      u1e <- EP.upsert u1 [OneUniqueName =. val "fifth"]
+      liftIO $ entityVal u1e `shouldBe` u1
+      u2e <- EP.upsert u2 [OneUniqueName =. val "fifth"]
+      liftIO $ entityVal u2e `shouldBe` u2
+      u3e <- EP.upsert u3 [OneUniqueName =. val "fifth"]
+      liftIO $ entityVal u3e `shouldBe` u1{oneUniqueName="fifth"}
 
 type JSONValue = Maybe (JSONB A.Value)
 
@@ -1021,6 +1049,8 @@ main = do
       testPostgresqlUpdate
       testPostgresqlCoalesce
       testPostgresqlTextFunctions
+      testInsertUniqueViolation
+      testUpsert
       describe "PostgreSQL JSON tests" $ do
         -- NOTE: We only clean the table once, so we
         -- can use its contents across all JSON tests
@@ -1053,7 +1083,9 @@ run_worker act = withConn $ runSqlConn (migrateIt >> act)
 migrateIt :: RunDbMonad m => SqlPersistT (R.ResourceT m) ()
 migrateIt = do
   void $ runMigrationSilent migrateAll
+  void $ runMigrationSilent migrateUnique
   cleanDB
+  cleanUniques
 
 withConn :: RunDbMonad m => (SqlBackend -> R.ResourceT m a) -> m a
 withConn =