The ability to learn and access new memories requires an intact hippocampal formation, a complex three-dimensional structure that spans the anterior-posterior aspect of the temporal lobe. Historically, the transverse axis has dominated studies exploring mnemonic properties of the hippocampus, but in the last decade the importance of the long axis has been coming into focus. Anatomical and physiological findings are reviewed suggesting that the long axis functions as a circuit. Recent imaging studies investigating the long axis as a circuit are summarized, pointing to specific mechanisms that can account for how the hippocampus associates separate sensory input during memory acquisition and recall.