Agents often interact strategically to meet conditions involving their own or other agents' knowledge. This interaction can be modeled using a new method of game construction, knowledge condition games, introduced in this paper. Knowledge condition games are games in which a coalition of agents chooses its strategy in an extensive game form such that an epistemic logic condition is fulfilled. In this paper knowledge condition games are defined and applied to two example problems involving voting and a quiz master problem. It is also shown that a restricted class of knowledge condition games is NP-complete.