Setup
An 8×8 board starts with four discs in the center: two black and two white, diagonally arranged. Black moves first.
Place a disc
You must place a disc on an empty square such that at least one straight line of opponent discs is flanked by your new disc and another one of your color.
Flip
All flanked opponent discs are flipped to your color. Lines are horizontal, vertical, or diagonal.
Pass
If you have no legal move, you must pass. If both players pass in a row, the game ends.
End
When the board is full or no one can move, whoever has more discs wins.