The understanding of the neuroanatomic substrates and cognitive processes underlying memory functioning has improved dramatically during the past several decades. Animal studies and observations of patients who have brain diseases show that memory is not a unitary factor but instead can be parsed into overlapping but dissociable constructs; that encoding, retention, and retrieval processes depend on the integrity of several distinct brain regions; and that the creation of new memories depends on structural and functional changes within the neuronal systems of those brain regions. Much remains to be learned, however, regarding the specific biologic,genetic, and information-processing mechanisms underlying many features of this complex cognitive construct. As this knowledge base grows, new and improved pharmacologic and behavioral treatments for patients who have memory disorders may be realized.