Bolster is a turn-based, abstract strategy game where two lords meet on the battlefield; both maneuvering to eliminate the other's most powerful units. Players move their units of various strengths to constantly improve their own position, while weakening their opponent. All units share the strength of adjacent allied units when resolving attacks/defense, and charge movements allow long chains of units to be moved to trap, manipulate, and eliminate their opponent’s units.
Each player takes one move per turn, and based on positions of allied and enemy pieces, attack and defense scores may be bolstered by adjacent units. Players may choose to have any number of allied units follow behind the piece moved.
The object of the game is to eliminate each of the opponents 3 most powerful units; when only one of the 3 most powerful units is left, that player must choose one of his remaining pieces to remove from play at the end of each turn.