The game starts with two black and two white pieces in the board's centre.
Black and white take turns to add pieces to the board. On your turn you must place a piece such that there is an unbroken line of opponent pieces between your added piece and another piece of your colour (horizontal, vertical or diagonal). When you place such a piece, flip the line of opposing pieces to your colour.
If you cannot place a piece, you must pass.
The game ends when the board is full, or when neither player can make a valid move. The game is won by player with the most pieces of their colour visible.