diff --git a/config.json b/config.json
index 5c32a837..648d32df 100644
--- a/config.json
+++ b/config.json
@@ -1244,6 +1244,14 @@
         "prerequisites": [],
         "difficulty": 6
       },
+      {
+        "slug": "state-of-tic-tac-toe",
+        "name": "State of Tic-Tac-Toe",
+        "uuid": "64ea517d-88ec-46db-b723-004681255580",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "food-chain",
         "name": "Food Chain",
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 00000000..f525d358
--- /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 00000000..7b0e3c6a
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/.meta/config.json
@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "tomasnorre"
+  ],
+  "files": {
+    "solution": [
+      "StateOfTicTacToe.php"
+    ],
+    "test": [
+      "StateOfTicTacToeTest.php"
+    ],
+    "example": [
+      ".meta/example.php"
+    ]
+  },
+  "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/example.php b/exercises/practice/state-of-tic-tac-toe/.meta/example.php
new file mode 100644
index 00000000..7f6f4122
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/.meta/example.php
@@ -0,0 +1,68 @@
+<?php
+
+declare(strict_types=1);
+
+enum State
+{
+    case Win;
+    case Ongoing;
+    case Draw;
+}
+
+class StateOfTicTacToe
+{
+    public function gameState(array $board): State
+    {
+        $xCount = $this->countPlayer($board, 'X');
+        $oCount = $this->countPlayer($board, 'O');
+
+        if ($xCount < $oCount) {
+            throw new \RuntimeException("Wrong turn order: O started");
+        }
+
+        if ($xCount !== $oCount && $xCount !== $oCount + 1) {
+            throw new \RuntimeException("Wrong turn order: X went twice");
+        }
+
+        $xWon = $this->hasWon($board, 'X');
+        $oWon = $this->hasWon($board, 'O');
+
+        if ($xWon && $oWon) {
+            throw new \RuntimeException("Impossible board: game should have ended after the game was won");
+        }
+
+        if ($xWon || $oWon) {
+            return State::Win;
+        }
+
+        if ($xCount + $oCount === 9) {
+            return State::Draw;
+        }
+
+        return State::Ongoing;
+    }
+
+    private function countPlayer(array $board, string $player): int
+    {
+        $count = 0;
+        foreach ($board as $row) {
+            foreach (str_split($row) as $cell) {
+                if ($cell === $player) {
+                    $count++;
+                }
+            }
+        }
+        return $count;
+    }
+
+    private function hasWon(array $board, string $player): bool
+    {
+        for ($i = 0; $i < 3; $i++) {
+            if (($board[$i][0] === $player && $board[$i][1] === $player && $board[$i][2] === $player) || ($board[0][$i] === $player && $board[1][$i] === $player && $board[2][$i] === $player)) {
+                return true;
+            }
+        }
+        // Check the diagonal
+        return ($board[0][0] === $player && $board[1][1] === $player && $board[2][2] === $player) || ($board[0][2] === $player && $board[1][1] === $player && $board[2][0] === $player);
+    }
+}
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 00000000..8fc25e21
--- /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/StateOfTicTacToe.php b/exercises/practice/state-of-tic-tac-toe/StateOfTicTacToe.php
new file mode 100644
index 00000000..821493d8
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/StateOfTicTacToe.php
@@ -0,0 +1,40 @@
+<?php
+
+/*
+ * By adding type hints and enabling strict type checking, code can become
+ * easier to read, self-documenting and reduce the number of potential bugs.
+ * By default, type declarations are non-strict, which means they will attempt
+ * to change the original type to match the type specified by the
+ * type-declaration.
+ *
+ * In other words, if you pass a string to a function requiring a float,
+ * it will attempt to convert the string value to a float.
+ *
+ * To enable strict mode, a single declare directive must be placed at the top
+ * of the file.
+ * This means that the strictness of typing is configured on a per-file basis.
+ * This directive not only affects the type declarations of parameters, but also
+ * a function's return type.
+ *
+ * For more info review the Concept on strict type checking in the PHP track
+ * <link>.
+ *
+ * To disable strict typing, comment out the directive below.
+ */
+
+declare(strict_types=1);
+
+enum State
+{
+    case Win;
+    case Ongoing;
+    case Draw;
+}
+
+class StateOfTicTacToe
+{
+    public function gameState(array $board): State
+    {
+        throw new \BadMethodCallException(sprintf('Implement the %s method', __FUNCTION__));
+    }
+}
diff --git a/exercises/practice/state-of-tic-tac-toe/StateOfTicTacToeTest.php b/exercises/practice/state-of-tic-tac-toe/StateOfTicTacToeTest.php
new file mode 100644
index 00000000..718a166a
--- /dev/null
+++ b/exercises/practice/state-of-tic-tac-toe/StateOfTicTacToeTest.php
@@ -0,0 +1,381 @@
+<?php
+
+declare(strict_types=1);
+
+class StateOfTicTacToeTest extends PHPUnit\Framework\TestCase
+{
+    private StateOfTicTacToe $stateOfTicTacToe;
+
+    public static function setUpBeforeClass(): void
+    {
+        require_once 'StateOfTicTacToe.php';
+    }
+
+    protected function setUp(): void
+    {
+        $this->stateOfTicTacToe = new StateOfTicTacToe();
+    }
+
+    /**
+     * uuid: fe8e9fa9-37af-4d7e-aa24-2f4b8517161a
+     */
+    public function testWonGamesFinishedGameWhereXWonViaLeftColumnVictory(): void
+    {
+        $board = [
+            "XOO",
+            "X  ",
+            "X  "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 96c30df5-ae23-4cf6-bf09-5ef056dddea1
+     */
+    public function testWonGameFinishedGameWhereXWonViaMiddleColumnVictory(): void
+    {
+        $board = [
+            "OXO",
+            " X ",
+            " X "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 0d7a4b0a-2afd-4a75-8389-5fb88ab05eda
+     */
+    public function testWonGameFinishedGameWhereXWonViaRightColumnVictory(): void
+    {
+        $board = [
+            "OOX",
+            "  X",
+            "  X"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: bd1007c0-ec5d-4c60-bb9f-1a4f22177d51
+     */
+    public function testWonGamesFinishedGameWhereOWonViaLeftColumnVictory(): void
+    {
+        $board = [
+            "OXX",
+            "OX ",
+            "O  "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: c032f800-5735-4354-b1b9-46f14d4ee955
+     */
+    public function testWonGameFinishedGameWhereOWonViaMiddleColumnVictory(): void
+    {
+        $board = [
+            "XOX",
+            " OX",
+            " O "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 662c8902-c94a-4c4c-9d9c-e8ca513db2b4
+     */
+    public function testWonGameFinishedGameWhereOWonViaRightColumnVictory(): void
+    {
+        $board = [
+            "XXO",
+            " XO",
+            "  O"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 2d62121f-7e3a-44a0-9032-0d73e3494941
+     */
+    public function testWonGameFinishedWhereXWonViaTopRowVictory(): void
+    {
+        $board = [
+            "XXX",
+            "XOO",
+            "O  "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 346527db-4db9-4a96-b262-d7023dc022b0
+     */
+    public function testWonGameFinishedWhereXWonViaMiddleRowVictory(): void
+    {
+        $board = [
+            "O  ",
+            "XXX",
+            " O "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: a013c583-75f8-4ab2-8d68-57688ff04574
+     */
+    public function testWonGameFinishedWhereXWonViaBottomRowVictory(): void
+    {
+        $board = [
+            " OO",
+            "O X",
+            "XXX"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 2c08e7d7-7d00-487f-9442-e7398c8f1727
+     */
+    public function testWonGameFinishedWhereOWonViaTopRowVictory(): void
+    {
+        $board = [
+            "OOO",
+            "XXO",
+            "XX "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: bb1d6c62-3e3f-4d1a-9766-f8803c8ed70f
+     */
+    public function testWonGameFinishedWhereOWonViaMiddleRowVictory(): void
+    {
+        $board = [
+            "XX ",
+            "OOO",
+            "X  "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 6ef641e9-12ec-44f5-a21c-660ea93907af
+     */
+    public function testWonGameFinishedWhereOWonViaBottomRowVictory(): void
+    {
+        $board = [
+            "XOX",
+            " XX",
+            "OOO"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: ab145b7b-26a7-426c-ab71-bf418cd07f81
+     */
+    public function testWonGameFinishedWhereXWonViaFallingDiagonalVictory(): void
+    {
+        $board = [
+            "XOO",
+            " X ",
+            "  X"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 7450caab-08f5-4f03-a74b-99b98c4b7a4b
+     */
+    public function testWonGameFinishedWhereXWonViaRisingDiagonalVictory(): void
+    {
+        $board = [
+            "O X",
+            "OX ",
+            "X  "
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: c2a652ee-2f93-48aa-a710-a70cd2edce61
+     */
+    public function testWonGameFinishedWhereOWonViaFallingDiagonalVictory(): void
+    {
+        $board = [
+            "OXX",
+            "OOX",
+            "X O"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 5b20ceea-494d-4f0c-a986-b99efc163bcf
+     */
+    public function testWonGameFinishedWhereOWonViaRisingDiagonalVictory(): void
+    {
+        $board = [
+            "  O",
+            " OX",
+            "OXX"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 035a49b9-dc35-47d3-9d7c-de197161b9d4
+     */
+    public function testWonGameFinishedGameWhereXWonViaARowAndAColumnVictory(): void
+    {
+        $board = [
+            "XXX",
+            "XOO",
+            "XOO"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: e5dfdeb0-d2bf-4b5a-b307-e673f69d4a53
+     */
+    public function testWonGameFinishedGameWhereXWonViaTwoDiagonalVictories(): void
+    {
+        $board = [
+            "XOX",
+            "OXO",
+            "XOX"
+        ];
+        $this->assertEquals(State::Win, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: b42ed767-194c-4364-b36e-efbfb3de8788
+     */
+    public function testDrawGame(): void
+    {
+        $board = [
+            "XOX",
+            "XXO",
+            "OXO"
+        ];
+        $this->assertEquals(State::Draw, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 227a76b2-0fef-4e16-a4bd-8f9d7e4c3b13
+     */
+    public function testAnotherDrawGame(): void
+    {
+        $board = [
+            "XXO",
+            "OXX",
+            "XOO"
+        ];
+        $this->assertEquals(State::Draw, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 4d93f15c-0c40-43d6-b966-418b040012a9
+     */
+    public function testOngoingGameOneMoveIn(): void
+    {
+        $board = [
+            "   ",
+            "X  ",
+            "   "
+        ];
+        $this->assertEquals(State::Ongoing, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: c407ae32-4c44-4989-b124-2890cf531f19
+     */
+    public function testOngoingGameTwoMovesIn(): void
+    {
+        $board = [
+            "O  ",
+            " X ",
+            "   "
+        ];
+        $this->assertEquals(State::Ongoing, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 199b7a8d-e2b6-4526-a85e-78b416e7a8a9
+     */
+    public function testOngoingGameFiveMovesIn(): void
+    {
+        $board = [
+            "X  ",
+            " XO",
+            "OX "
+        ];
+        $this->assertEquals(State::Ongoing, $this->stateOfTicTacToe->gameState($board));
+    }
+
+    /**
+     * uuid: 1670145b-1e3d-4269-a7eb-53cd327b302e
+     */
+    public function testInvalidBoardsXWentTwice(): void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage("Wrong turn order: X went twice");
+
+        $board = [
+            "XX ",
+            "   ",
+            "   "
+        ];
+        $this->stateOfTicTacToe->gameState($board);
+    }
+
+    /**
+     * uuid: 47c048e8-b404-4bcf-9e51-8acbb3253f3b
+     */
+    public function testInvalidBoardOStarted(): void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage("Wrong turn order: O started");
+
+        $board = [
+            "OOX",
+            "   ",
+            "   "
+        ];
+        $this->stateOfTicTacToe->gameState($board);
+    }
+
+    /**
+     * uuid: 6c1920f2-ab5c-4648-a0c9-997414dda5eb
+     */
+    public function testInvalidBoard(): void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage("Impossible board: game should have ended after the game was won");
+
+        $board = [
+            "XXX",
+            "OOO",
+            "   "
+        ];
+        $this->stateOfTicTacToe->gameState($board);
+    }
+
+    /**
+     * uuid: 4801cda2-f5b7-4c36-8317-3cdd167ac22c
+     */
+    public function testInvalidBoardPlayersKeptPlayingAfterAWin(): void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage("Impossible board: game should have ended after the game was won");
+
+        $board = [
+            "XXX",
+            "OOO",
+            "XOX"
+        ];
+        $this->stateOfTicTacToe->gameState($board);
+    }
+}