The board and the starting position
Othello is played on a board of 8 by 8, 64 squares in all. The game starts with two black and two white discs placed diagonally on the four center squares, and Black moves first.
How to play: trapped discs are flipped
When you place a disc, you must trap a line of opponent discs between the new disc and a disc of your own already on the board. All the trapped opponent discs are flipped to your color. This works in all 8 directions, horizontal, vertical and diagonal, and one move can flip discs in several directions at once.
You cannot play on a square where no opponent disc would be flipped.
If an empty square or one of your own discs breaks the line, the opponent discs beyond it are not flipped. Only lines running directly from the disc you just placed are flipped, and flipped discs do not cause further flips in a chain. You cannot choose to flip only some of them: all flippable discs must be flipped.
Exercise
White to move. Where can White flip the most Black discs? The small squares show where White can play.
Try it yourself
Take turns playing Black and White on the board below. Small squares mark the legal moves.
Passing
If you have no square to play on, you pass and your opponent plays again. You cannot pass on purpose when you have a move. A player who passed plays again as soon as a move becomes available.
The end of the game and the winner
The game ends when the board is full or when neither Black nor White can move. The player with more discs on the board wins. If the counts are equal, the game is a draw.