What relation between an experience and a physical object makes the experience a perception of the object?1 One common answer is that it is a certain kind of causal relation. The idea is that to perceive an object is just to undergo an experience appropriately caused by the object. This answer is incorrect. The reason is that perceiving an object does not supervene on the causal connection the object bears to the perceiver's experience. Whether or not a person perceives an object depends, in part, on conditions that could obtain or fail to obtain without variation in the causal processes (if any) by which the object causes the person's experience. In what follows, I explain and defend these claims.