Abstract: Mental practice is the cognitive rehearsal of a task prior to performance. Although most researchers contend that mental practice is an effective means of enhancing performance, a clear consensus is precluded because (1) mental practice is often defined so loosely as to include almost any type of mental preparation and (2) empirical results are inconclusive. A meta-analysis of the literature on mental practice was conducted to determine the effect of mental practice on performance and to identify conditions under which mental practice is most effective. Results indicate that mental practice has a positive and significant effect on performance, and the effectiveness of mental practice is moderated by the type of task, the retention interval between practice and performance, and the length or duration of the mental practice intervention.