diff --git a/config.json b/config.json
index db4619c53..145ade90f 100644
--- a/config.json
+++ b/config.json
@@ -413,6 +413,17 @@
           "maybe"
         ]
       },
+      {
+        "slug": "state-of-tic-tac-toe",
+        "name": "State of Tic-Tac-Toe",
+        "uuid": "adc12fee-2e2f-4704-abbc-b5acddebd97e",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4,
+        "topics": [
+          "strings"
+        ]
+      },
       {
         "slug": "word-count",
         "name": "Word Count",
diff --git a/exercises/practice/state-of-tic-tac-toe/.docs/instructions.md b/exercises/practice/state-of-tic-tac-toe/.docs/instructions.md
new file mode 100644
index 000000000..f525d3585
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/.docs/instructions.md
@@ -0,0 +1,101 @@
+# Instructions
+
+In this exercise, you're going to implement a program that determines the state of a [tic-tac-toe][] game.
+(_You may also know the game as "noughts and crosses" or "Xs and Os"._)
+
+The games is played on a 3×3 grid.
+Players take turns to place `X`s and `O`s on the grid.
+The game ends when one player has won by placing three of marks in a row, column, or along a diagonal of the grid, or when the entire grid is filled up.
+
+In this exercise, we will assume that `X` starts.
+
+It's your job to determine which state a given game is in.
+
+There are 3 potential game states:
+
+- The game is **ongoing**.
+- The game ended in a **draw**.
+- The game ended in a **win**.
+
+If the given board is invalid, throw an appropriate error.
+
+If a board meets the following conditions, it is invalid:
+
+- The given board cannot be reached when turns are taken in the correct order (remember that `X` starts).
+- The game was played after it already ended.
+
+## Examples
+
+### Ongoing game
+
+```text
+   |   |
+ X |   |
+___|___|___
+   |   |
+   | X | O
+___|___|___
+   |   |
+ O | X |
+   |   |
+```
+
+### Draw
+
+```text
+   |   |
+ X | O | X
+___|___|___
+   |   |
+ X | X | O
+___|___|___
+   |   |
+ O | X | O
+   |   |
+```
+
+### Win
+
+```text
+   |   |
+ X | X | X
+___|___|___
+   |   |
+   | O | O
+___|___|___
+   |   |
+   |   |
+   |   |
+```
+
+### Invalid
+
+#### Wrong turn order
+
+```text
+   |   |
+ O | O | X
+___|___|___
+   |   |
+   |   |
+___|___|___
+   |   |
+   |   |
+   |   |
+```
+
+#### Continued playing after win
+
+```text
+   |   |
+ X | X | X
+___|___|___
+   |   |
+ O | O | O
+___|___|___
+   |   |
+   |   |
+   |   |
+```
+
+[tic-tac-toe]: https://en.wikipedia.org/wiki/Tic-tac-toe
diff --git a/exercises/practice/state-of-tic-tac-toe/.meta/config.json b/exercises/practice/state-of-tic-tac-toe/.meta/config.json
new file mode 100644
index 000000000..b98b0f4ee
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/.meta/config.json
@@ -0,0 +1,23 @@
+{
+  "authors": [
+    "tofische"
+  ],
+  "files": {
+    "solution": [
+      "src/StateOfTicTacToe.hs",
+      "package.yaml"
+    ],
+    "test": [
+      "test/Tests.hs"
+    ],
+    "example": [
+      ".meta/examples/success-standard/src/StateOfTicTacToe.hs"
+    ],
+    "invalidator": [
+      "stack.yaml"
+    ]
+  },
+  "blurb": "Determine the game state of a match of Tic-Tac-Toe.",
+  "source": "Created by Sascha Mann for the Julia track of the Exercism Research Experiment.",
+  "source_url": "https://github.com/exercism/research_experiment_1/tree/julia-dev/exercises/julia-1-a"
+}
diff --git a/exercises/practice/state-of-tic-tac-toe/.meta/examples/success-standard/package.yaml b/exercises/practice/state-of-tic-tac-toe/.meta/examples/success-standard/package.yaml
new file mode 100644
index 000000000..5a09abeea
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/.meta/examples/success-standard/package.yaml
@@ -0,0 +1,20 @@
+name: state-of-tic-tac-toe
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: StateOfTicTacToe
+  source-dirs: src
+  ghc-options: -Wall
+  # dependencies:
+  # - foo       # List here the packages you
+  # - bar       # want to use in your solution.
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+    - state-of-tic-tac-toe
+    - hspec
diff --git a/exercises/practice/state-of-tic-tac-toe/.meta/examples/success-standard/src/StateOfTicTacToe.hs b/exercises/practice/state-of-tic-tac-toe/.meta/examples/success-standard/src/StateOfTicTacToe.hs
new file mode 100644
index 000000000..6160fc8b9
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/.meta/examples/success-standard/src/StateOfTicTacToe.hs
@@ -0,0 +1,30 @@
+module StateOfTicTacToe (gameState, GameState(..)) where
+
+import Data.List (transpose)
+
+data GameState = WinX | WinO | Draw | Ongoing | Impossible deriving (Eq, Show)
+
+gameState :: [String] -> GameState
+gameState board
+    | countO > countX          = Impossible
+    | countX > countO + 1      = Impossible
+    | winO && countX > countO  = Impossible
+    | winX && countO >= countX = Impossible
+    | winX                     = WinX
+    | winO                     = WinO
+    | countO + countX == 9     = Draw
+    | otherwise                = Ongoing
+    where
+        transposedBoard = transpose board
+        fallingDiag = zipWith (!!) board [0..]
+        risingDiag = zipWith (!!) (reverse board) [0..]
+        countX = count 'X'
+        countO = count 'O'
+        winX = win 'X'
+        winO = win 'O'
+        count ch = length $ filter (== ch) $ concat board
+        win ch =
+            any (all (== ch)) board ||
+            any (all (== ch)) transposedBoard ||
+            all (==ch) fallingDiag ||
+            all (==ch) risingDiag
diff --git a/exercises/practice/state-of-tic-tac-toe/.meta/tests.toml b/exercises/practice/state-of-tic-tac-toe/.meta/tests.toml
new file mode 100644
index 000000000..8fc25e211
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/.meta/tests.toml
@@ -0,0 +1,101 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[fe8e9fa9-37af-4d7e-aa24-2f4b8517161a]
+description = "Won games -> Finished game where X won via left column victory"
+
+[96c30df5-ae23-4cf6-bf09-5ef056dddea1]
+description = "Won games -> Finished game where X won via middle column victory"
+
+[0d7a4b0a-2afd-4a75-8389-5fb88ab05eda]
+description = "Won games -> Finished game where X won via right column victory"
+
+[bd1007c0-ec5d-4c60-bb9f-1a4f22177d51]
+description = "Won games -> Finished game where O won via left column victory"
+
+[c032f800-5735-4354-b1b9-46f14d4ee955]
+description = "Won games -> Finished game where O won via middle column victory"
+
+[662c8902-c94a-4c4c-9d9c-e8ca513db2b4]
+description = "Won games -> Finished game where O won via right column victory"
+
+[2d62121f-7e3a-44a0-9032-0d73e3494941]
+description = "Won games -> Finished game where X won via top row victory"
+
+[108a5e82-cc61-409f-aece-d7a18c1beceb]
+description = "Won games -> Finished game where X won via middle row victory"
+include = false
+
+[346527db-4db9-4a96-b262-d7023dc022b0]
+description = "Won games -> Finished game where X won via middle row victory"
+reimplements = "108a5e82-cc61-409f-aece-d7a18c1beceb"
+
+[a013c583-75f8-4ab2-8d68-57688ff04574]
+description = "Won games -> Finished game where X won via bottom row victory"
+
+[2c08e7d7-7d00-487f-9442-e7398c8f1727]
+description = "Won games -> Finished game where O won via top row victory"
+
+[bb1d6c62-3e3f-4d1a-9766-f8803c8ed70f]
+description = "Won games -> Finished game where O won via middle row victory"
+
+[6ef641e9-12ec-44f5-a21c-660ea93907af]
+description = "Won games -> Finished game where O won via bottom row victory"
+
+[ab145b7b-26a7-426c-ab71-bf418cd07f81]
+description = "Won games -> Finished game where X won via falling diagonal victory"
+
+[7450caab-08f5-4f03-a74b-99b98c4b7a4b]
+description = "Won games -> Finished game where X won via rising diagonal victory"
+
+[c2a652ee-2f93-48aa-a710-a70cd2edce61]
+description = "Won games -> Finished game where O won via falling diagonal victory"
+
+[5b20ceea-494d-4f0c-a986-b99efc163bcf]
+description = "Won games -> Finished game where O won via rising diagonal victory"
+
+[035a49b9-dc35-47d3-9d7c-de197161b9d4]
+description = "Won games -> Finished game where X won via a row and a column victory"
+
+[e5dfdeb0-d2bf-4b5a-b307-e673f69d4a53]
+description = "Won games -> Finished game where X won via two diagonal victories"
+
+[b42ed767-194c-4364-b36e-efbfb3de8788]
+description = "Drawn games -> Draw"
+
+[227a76b2-0fef-4e16-a4bd-8f9d7e4c3b13]
+description = "Drawn games -> Another draw"
+
+[4d93f15c-0c40-43d6-b966-418b040012a9]
+description = "Ongoing games -> Ongoing game: one move in"
+
+[c407ae32-4c44-4989-b124-2890cf531f19]
+description = "Ongoing games -> Ongoing game: two moves in"
+
+[199b7a8d-e2b6-4526-a85e-78b416e7a8a9]
+description = "Ongoing games -> Ongoing game: five moves in"
+
+[1670145b-1e3d-4269-a7eb-53cd327b302e]
+description = "Invalid boards -> Invalid board: X went twice"
+
+[47c048e8-b404-4bcf-9e51-8acbb3253f3b]
+description = "Invalid boards -> Invalid board: O started"
+
+[b1dc8b13-46c4-47db-a96d-aa90eedc4e8d]
+description = "Invalid boards -> Invalid board"
+include = false
+
+[6c1920f2-ab5c-4648-a0c9-997414dda5eb]
+description = "Invalid boards -> Invalid board: X won and O kept playing"
+reimplements = "b1dc8b13-46c4-47db-a96d-aa90eedc4e8d"
+
+[4801cda2-f5b7-4c36-8317-3cdd167ac22c]
+description = "Invalid boards -> Invalid board: players kept playing after a win"
diff --git a/exercises/practice/state-of-tic-tac-toe/package.yaml b/exercises/practice/state-of-tic-tac-toe/package.yaml
new file mode 100644
index 000000000..39dbd6829
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/package.yaml
@@ -0,0 +1,21 @@
+name: state-of-tic-tac-toe
+version: 1.0.0.0
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: StateOfTicTacToe
+  source-dirs: src
+  ghc-options: -Wall
+  # dependencies:
+  # - foo       # List here the packages you
+  # - bar       # want to use in your solution.
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - state-of-tic-tac-toe
+      - hspec
diff --git a/exercises/practice/state-of-tic-tac-toe/src/StateOfTicTacToe.hs b/exercises/practice/state-of-tic-tac-toe/src/StateOfTicTacToe.hs
new file mode 100644
index 000000000..2b1b83bc4
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/src/StateOfTicTacToe.hs
@@ -0,0 +1,6 @@
+module StateOfTicTacToe (gameState, GameState(..)) where
+
+data GameState = WinX | WinO | Draw | Ongoing | Impossible deriving (Eq, Show)
+
+gameState :: [String] -> GameState
+gameState board = error "You need to implement this function."
diff --git a/exercises/practice/state-of-tic-tac-toe/stack.yaml b/exercises/practice/state-of-tic-tac-toe/stack.yaml
new file mode 100644
index 000000000..115878212
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/stack.yaml
@@ -0,0 +1 @@
+resolver: lts-20.18
diff --git a/exercises/practice/state-of-tic-tac-toe/test/Tests.hs b/exercises/practice/state-of-tic-tac-toe/test/Tests.hs
new file mode 100644
index 000000000..d11fa197d
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/test/Tests.hs
@@ -0,0 +1,131 @@
+{-# LANGUAGE RecordWildCards #-}
+
+import Data.Foldable     (for_)
+import Test.Hspec        (Spec, describe, it, shouldBe)
+import Test.Hspec.Runner (configFailFast, defaultConfig, hspecWith)
+
+import StateOfTicTacToe (gameState, GameState(..))
+
+main :: IO ()
+main = hspecWith defaultConfig {configFailFast = True} specs
+
+specs :: Spec
+specs = describe "measure" $ for_ cases test
+  where
+    test Case{..} = it description $ gameState board `shouldBe` expected
+ 
+data Case = Case { description :: String
+                 , board       :: [String]
+                 , expected    :: GameState
+                 }
+
+cases :: [Case]
+cases = [ Case { description = "Finished game where X won via left column victory"
+               , board = ["XOO", "X  ", "X  "]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where X won via middle column victory"
+               , board = ["OXO", " X ", " X "]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where X won via right column victory"
+               , board = ["OOX", "  X", "  X"]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where O won via left column victory"
+               , board = ["OXX", "OX ", "O  "]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where O won via middle column victory"
+               , board = ["XOX", " OX", " O "]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where O won via right column victory"
+               , board = ["XXO", " XO", "  O"]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where X won via top row victory"
+               , board = ["XXX", "XOO", "O  "]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where X won via middle row victory"
+               , board = ["O  ", "XXX", " O "]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where X won via bottom row victory"
+               , board = [" OO", "O X", "XXX"]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where O won via top row victory"
+               , board = ["OOO", "XXO", "XX "]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where O won via middle row victory"
+               , board = ["XX ", "OOO", "X  "]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where O won via bottom row victory"
+               , board = ["XOX", " XX", "OOO"]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where X won via falling diagonal victory"
+               , board = ["XOO", " X ", "  X"]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where X won via rising diagonal victory"
+               , board = ["O X", "OX ", "X  "]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where O won via falling diagonal victory"
+               , board = ["OXX", "OOX", "X O"]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where O won via rising diagonal victory"
+               , board = ["  O", " OX", "OXX"]
+               , expected = WinO
+               }
+        , Case { description = "Finished game where X won via a row and a column victory"
+               , board = ["XXX", "XOO", "XOO"]
+               , expected = WinX
+               }
+        , Case { description = "Finished game where X won via two diagonal victories"
+               , board = ["XOX", "OXO", "XOX"]
+               , expected = WinX
+               }
+        , Case { description = "Drawn"
+               , board = ["XOX", "XXO", "OXO"]
+               , expected = Draw
+               }
+        , Case { description = "Another draw"
+               , board = ["XXO", "OXX", "XOO"]
+               , expected = Draw
+               }
+        , Case { description = "Ongoing game: one move in"
+               , board = ["   ", "X  ", "   "]
+               , expected = Ongoing
+               }
+        , Case { description = "Ongoing game: two moves in"
+               , board = ["O  ", " X ", "   "]
+               , expected = Ongoing
+               }
+        , Case { description = "Ongoing game: five moves in"
+               , board = ["X  ", " XO", "OX "]
+               , expected = Ongoing
+               }
+        , Case { description = "Invalid board: X went twice"
+               , board = ["XX ", "   ", "   "]
+               , expected = Impossible
+               }
+        , Case { description = "Invalid board: O started"
+               , board = ["OOX", "   ", "   "]
+               , expected = Impossible
+               }
+        , Case { description = "Invalid board: X won and O kept playing"
+               , board = ["XXX", "OOO", "   "]
+               , expected = Impossible
+               }
+        , Case { description = "Invalid board: players kept playing after a win"
+               , board = ["XXX", "OOO", "XOX"]
+               , expected = Impossible
+               }
+        ]