Prospective memory or memory for actions to be performed in the future is critical to everyday life and yet has been virtually ignored by researchers until recently. Relative to typically studied retrospective memory tasks, prospective memory retrieval is self-initiated in the sense that a person must remember to perform an intended action without an external request to search memory. This self-initiated characteristic has implications for understanding how retrieval occurs, the storage dynamics of prospective memories, and the optimal encoding strategies. We comprehensively review major theories and evidence on these issues as well as explore developmental changes in prospective memory. Finally, we review the neural processes underlying prospective memory.