diff --git a/contracts/src/Counter.sol b/contracts/src/Counter.sol
deleted file mode 100644
index aded7997..00000000
--- a/contracts/src/Counter.sol
+++ /dev/null
@@ -1,14 +0,0 @@
-// SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.8.13;
-
-contract Counter {
-    uint256 public number;
-
-    function setNumber(uint256 newNumber) public {
-        number = newNumber;
-    }
-
-    function increment() public {
-        number++;
-    }
-}
diff --git a/contracts/src/TicTacToe.sol b/contracts/src/TicTacToe.sol
new file mode 100644
index 00000000..add6d79e
--- /dev/null
+++ b/contracts/src/TicTacToe.sol
@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.13;
+
+contract TicTacToe {
+    enum PlayerTurn { PlayerOne, PlayerTwo }
+
+    enum GameState {
+        WaitingForPlayer,
+        Playing,
+        Draw,
+        PlayerOneWins,
+        PlayerTwoWins
+    }
+
+    event GameCreated(uint256 indexed gameId, address indexed creator);
+    event PlayerJoinedGame(uint256 indexed gameId, address indexed player);
+    event PlayerMadeMove(uint256 indexed gameId, uint8 x, uint8 y);
+    event GameCompletedWithWinner(uint256 indexed gameId, address indexed winner);
+    event GameCompletedDraw(uint256 indexed gameId);
+
+    struct Game {
+        uint256 id;
+        GameState state;
+        address player1;
+        address player2;
+        PlayerTurn currentTurn;
+        address winner;
+        uint8 numOfTurns;
+        uint8[3][3] board;
+    }
+
+    uint256 numOfGames;
+    mapping(uint256 => Game) public games;
+    
+    // Magic Square: https://mathworld.wolfram.com/MagicSquare.html
+    uint8[3][3] private MAGIC_SQUARE = [[8, 3, 4], [1, 5, 9], [6, 7, 2]];
+    uint8 private constant MAGIC_SUM_PLAYER_ONE = 15;
+    uint8 private constant MAGIC_SUM_PLAYER_TWO = 30;
+
+    modifier validGame(uint256 gameId) {
+        require(gameId <= numOfGames, "Invalid game id");
+        _;
+    }
+
+    function createGame(address player1) public returns (uint256) {
+        numOfGames++;
+
+        games[numOfGames] = Game({
+            id: numOfGames,
+            state: GameState.WaitingForPlayer,
+            player1: player1,
+            player2: address(0),
+            currentTurn: PlayerTurn.PlayerOne,
+            winner: address(0),
+            numOfTurns: 0,
+            board: [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
+        });
+
+        emit GameCreated(numOfGames, player1);
+        return numOfGames;
+    }
+
+    function joinGame(address player2, uint256 gameId) public validGame(gameId) returns (bool) {    
+        Game storage game = games[gameId];
+
+        require(game.state == GameState.WaitingForPlayer, "Game already has enough players");
+        require(game.player1 != player2, "Players must be different");
+
+        game.player2 = player2;
+        game.state = GameState.Playing;
+        emit PlayerJoinedGame(game.id, game.player2);
+
+        return true;
+    }
+
+    function makeMove(address player, uint256 gameId, uint8 x, uint8 y) public validGame(gameId) returns (bool) {
+        Game storage game = games[gameId];
+        require(game.state == GameState.Playing, "Game hasn't started or has already been completed");
+    
+        bool isPlayerOneTurn = game.currentTurn == PlayerTurn.PlayerOne;
+        require(isPlayerOneTurn ? player == game.player1 : player == game.player2, "Not a valid player in the game");
+        require(x >= 0 && x <= 2 || y >= 0 && y <= 2, "Move out of bounds");
+        require(game.board[x][y] == 0, "Invalid move");
+
+        game.board[x][y] = isPlayerOneTurn ? 1 : 2;
+        game.currentTurn = isPlayerOneTurn ? PlayerTurn.PlayerTwo : PlayerTurn.PlayerOne;
+        game.numOfTurns++;
+        emit PlayerMadeMove(game.id, x, y);
+
+        bool isWin = checkForWin(player, game.id);
+        if (isWin) {
+            game.state = isPlayerOneTurn ? GameState.PlayerOneWins : GameState.PlayerTwoWins;
+            emit GameCompletedWithWinner(game.id, player);
+        } else if (game.numOfTurns >= 9) {
+            game.state = GameState.Draw;
+            emit GameCompletedDraw(game.id);
+        }
+
+        return true;
+    }
+
+    function getGame(uint256 gameId) public view returns (Game memory) {
+        return games[gameId];
+    }
+
+    function checkForWin(address player, uint256 gameId) public validGame(gameId) view returns (bool) {
+        Game storage game = games[gameId];
+        require(player == game.player1 || player == game.player2, "Not a valid player in the game");
+
+        uint8 magicSum = player == game.player1 ? MAGIC_SUM_PLAYER_ONE : MAGIC_SUM_PLAYER_TWO;
+
+        // row & col check
+        for (uint8 i = 0; i < 3; i++) {
+            uint8 rowSum = (game.board[i][0] * MAGIC_SQUARE[i][0]) + (game.board[i][1] * MAGIC_SQUARE[i][1]) + (game.board[i][2] * MAGIC_SQUARE[i][2]);
+            uint8 colSum = (game.board[0][i] * MAGIC_SQUARE[0][i]) + (game.board[1][i] * MAGIC_SQUARE[1][i]) + (game.board[2][i] * MAGIC_SQUARE[2][i]);
+
+            if (rowSum == magicSum || colSum == magicSum) {
+                return true;
+            }
+        }
+
+        // diag check
+        uint8 leftToRightSum = (game.board[0][0] * MAGIC_SQUARE[0][0]) + (game.board[1][1] * MAGIC_SQUARE[1][1]) + (game.board[2][2] * MAGIC_SQUARE[2][2]);
+        uint8 rightToLeftSum = (game.board[0][2] * MAGIC_SQUARE[0][2]) + (game.board[1][1] * MAGIC_SQUARE[1][1]) + (game.board[2][0] * MAGIC_SQUARE[2][0]);
+        if (leftToRightSum == magicSum || rightToLeftSum == magicSum) {
+            return true;
+        }
+
+        return false;
+    }
+}
diff --git a/contracts/test/Counter.t.sol b/contracts/test/Counter.t.sol
deleted file mode 100644
index 54b724f7..00000000
--- a/contracts/test/Counter.t.sol
+++ /dev/null
@@ -1,24 +0,0 @@
-// SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.8.13;
-
-import {Test, console} from "forge-std/Test.sol";
-import {Counter} from "../src/Counter.sol";
-
-contract CounterTest is Test {
-    Counter public counter;
-
-    function setUp() public {
-        counter = new Counter();
-        counter.setNumber(0);
-    }
-
-    function test_Increment() public {
-        counter.increment();
-        assertEq(counter.number(), 1);
-    }
-
-    function testFuzz_SetNumber(uint256 x) public {
-        counter.setNumber(x);
-        assertEq(counter.number(), x);
-    }
-}
diff --git a/contracts/test/TicTacToe.t.sol b/contracts/test/TicTacToe.t.sol
new file mode 100644
index 00000000..abd3f5d1
--- /dev/null
+++ b/contracts/test/TicTacToe.t.sol
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.13;
+
+import {Test, console} from "forge-std/Test.sol";
+import {TicTacToe} from "../src/TicTacToe.sol";
+
+contract TicTacToeTest is Test {
+    address player1 = address(1);
+    address player2 = address(2);
+
+    function test_CreateGame() public {
+        TicTacToe ticTacToe = new TicTacToe();
+        uint256 gameId = ticTacToe.createGame(player1);
+        TicTacToe.Game memory game = ticTacToe.getGame(gameId);
+        assertEq(gameId, game.id);
+        assertEq(game.player1, player1);
+        assertEq(uint(game.state), uint(TicTacToe.GameState.WaitingForPlayer));
+    }
+
+    function test_JoinGameSuccessful() public {
+        TicTacToe ticTacToe = new TicTacToe();
+        uint256 gameId = ticTacToe.createGame(player1);
+
+        bool success = ticTacToe.joinGame(player2, gameId);
+        assertTrue(success);
+
+        TicTacToe.Game memory game = ticTacToe.getGame(gameId);
+        assertEq(game.player1, player1);
+        assertEq(game.player2, player2);
+    }
+
+    function test_JoinGameInvalidState() public {
+        TicTacToe ticTacToe = new TicTacToe();
+        uint256 gameId = ticTacToe.createGame(player1);
+        ticTacToe.joinGame(player2, gameId);
+        vm.expectRevert("Game already has enough players");
+        ticTacToe.joinGame(address(3), gameId);
+    }
+
+    function test_JoinGameSamePlayer() public {
+        TicTacToe ticTacToe = new TicTacToe();
+        uint256 gameId = ticTacToe.createGame(player1);
+        vm.expectRevert("Players must be different");
+        ticTacToe.joinGame(player1, gameId);
+    }
+
+    function test_PlayGameUntilWin() public {
+        TicTacToe ticTacToe = new TicTacToe();
+
+        // Game 1: row win by player 1
+        uint256 gameId = ticTacToe.createGame(player1);
+        ticTacToe.joinGame(player2, gameId);
+        ticTacToe.makeMove(player1, gameId, 0, 0);
+        ticTacToe.makeMove(player2, gameId, 1, 0);
+        ticTacToe.makeMove(player1, gameId, 0, 1);
+        ticTacToe.makeMove(player2, gameId, 1, 1);
+        ticTacToe.makeMove(player1, gameId, 0, 2);
+        TicTacToe.Game memory game = ticTacToe.getGame(gameId);
+        assertEq(uint(game.state), uint(TicTacToe.GameState.PlayerOneWins));
+
+        // Game 2: col win by player 2
+        gameId = ticTacToe.createGame(player1);
+        ticTacToe.joinGame(player2, gameId);
+        ticTacToe.makeMove(player1, gameId, 0, 0);
+        ticTacToe.makeMove(player2, gameId, 0, 1);
+        ticTacToe.makeMove(player1, gameId, 0, 2);
+        ticTacToe.makeMove(player2, gameId, 1, 1);
+        ticTacToe.makeMove(player1, gameId, 1, 0);
+        ticTacToe.makeMove(player2, gameId, 2, 1);
+        game = ticTacToe.getGame(gameId);
+        assertEq(uint(game.state), uint(TicTacToe.GameState.PlayerTwoWins));
+    
+        // Game 3: dial win by player 1
+        gameId = ticTacToe.createGame(player1);
+        ticTacToe.joinGame(player2, gameId);
+        ticTacToe.makeMove(player1, gameId, 0, 0);
+        ticTacToe.makeMove(player2, gameId, 1, 0);
+        ticTacToe.makeMove(player1, gameId, 1, 1);
+        ticTacToe.makeMove(player2, gameId, 1, 2);
+        ticTacToe.makeMove(player1, gameId, 2, 2);
+        game = ticTacToe.getGame(gameId);
+        assertEq(uint(game.state), uint(TicTacToe.GameState.PlayerOneWins));
+    }
+
+    function test_PlayGameUntilDraw() public {
+        TicTacToe ticTacToe = new TicTacToe();
+        uint256 gameId = ticTacToe.createGame(player1);
+        ticTacToe.joinGame(player2, gameId);
+        ticTacToe.makeMove(player1, gameId, 0, 1);
+        ticTacToe.makeMove(player2, gameId, 0, 0);
+        ticTacToe.makeMove(player1, gameId, 1, 0);
+        ticTacToe.makeMove(player2, gameId, 0, 2);
+        ticTacToe.makeMove(player1, gameId, 1, 2);
+        ticTacToe.makeMove(player2, gameId, 1, 1);
+        ticTacToe.makeMove(player1, gameId, 2, 0);
+        ticTacToe.makeMove(player2, gameId, 2, 1);
+        ticTacToe.makeMove(player1, gameId, 2, 2);
+        TicTacToe.Game memory game = ticTacToe.getGame(gameId);
+        assertEq(uint(game.state), uint(TicTacToe.GameState.Draw));
+    }
+}