From the instructions:PerPlexus is a game requiring both quick thinking and a constantly changing strategy. The play board is a network comprised of 6 sliding play pieces or shuttles that can be moved right or left, offensively or defensively, by either player. The game objective is to place 5 stones in a row -- horizontally, vertically, or diagonally -- while blocking the opponent's attempts to line up 6 stones in a row. Each shuttle has spaces for 7 stones. PerPlexus requires that a player plan moves several turns in advance whether playing stones or moving shuttles. - BoardGameGeek