In two experiments, subjects heard simple action statements (e.g., "Break the toothpick"), and, in some conditions, they also performed the action or imagined performing the action. In a second session that occurred at a later point (10 min, 24 h, 1 week, or 2 weeks later), subjects imagined performing actions one, three, or fivetimes. Some imagined actions represented statements heard, imagined, or performed in the first session, whereas other statements were new in the second session. During a third (test) phase, subjects were instructed to recognize statements only if they had occurred during the first session and, if recognized, to tell whether the action statement had been carried out, imagined, or merely heard. The primary finding was that increasing the number of imaginings during the second session caused subjects to remember later that they had performed an action during the first session when in fact they had not (imagination inflation). This outcome occurred both for statements that subjects had heard but not performed during the first session and for statements that had never been heard during the first session. The results are generally consistent with Johnson, Hashtroudi, and Lindsay's (1993) source monitoring framework and reveal a powerful memory illusion: Imagining performance of an action can cause its recollection as actually having been carried out.Imagery has long been known to exert powerful effects on remembering. The ancient Greeks discovered that imagining items in particular locations was an aid to remembering them and experimental psychologists have long studied the power of imagery as an aid to remembering (e.g., Bower, 1970;Paivio, 1969Paivio, , 1986. Ofcourse, when imagery is used as a mnemonic technique, the interest is in improving recollection for facts or events that the rememberer would like to recall at some later point. However, people use imagery for many other purposesin daydreaming, in fantasies, in setting goals, in wishing for future events, and in thinking about past events. The question we ask in the present paper is whether imagining might have deleterious consequences for memory, as well as the oft-noted positive effects. Briefly, the question we ask is: If people imagine performing some action, might they later remember that they actually did it?