The game starts with the board empty. Players take turns placing pieces on any empty intersection. After all eighteen pieces have been placed, players take turns moving. A move consists of sliding a piece along one of the board lines to an adjacent intersection. If a move in either phase of play results in three collinear pieces of the same color, then any one of the opponent's pieces may be removed from the board, unless that piece is currently forming a 3 in a row and there are other pieces of the opponent's color still on the board. An ideal position, which typically results in a win, is to be able to shuttle one piece back and forth between two mills, removing a piece every turn. 

Once a player has been reduced to two pieces, they are unable to capture any more of their opponent's pieces, and therefore that player loses the game. A common variant of nine men's morris adds four diagonal lines to the board. This makes the game faster and more tactical. The number of legal positions in nine men's morris is estimated to be 10¹⁰, the total number of possible games is approximately 10⁵⁰ .