The time course of forgetting was first rigorously analyzed by Ebbinghaus (1885). His famous savings function showed that the rate of forgetting continuously declines with the passage of time (a property later enshrined as the ?power law of forgetting?). Although not widely appreciated, this property of forgetting is consistent with Jost's (1897) venerable law of forgetting, which states that if two memories have the same strength, but one was formed more recently than the other, then, going forward, the younger trace will decay more rapidly than the older one. These long-established properties of forgetting (of interest mainly to experimental psychologists) may reflect the outcome of cellular and systems consolidation processes (of interest mainly to neuroscientists). Cellular consolidation takes place in the hippocampus in the hours after learning and serves to stabilize the memory trace (a process that may involve structural changes in hippocampal neurons). Systems consolidation refers to a more protracted process by which memories become independent of the hippocampus as they are established in cortical neurons (a process that may involve neural replay). Both forms of consolidation may opportunistically occur whenever the hippocampus is not engaged in the encoding of new information (e.g., during slow-wave sleep or quiet wake). One effect of consolidation may be to render the memory trace more resistant to interference that will occur once encoding resumes. This ?trace hardening? process may help to explain the otherwise mysterious properties of forgetting that were identified by Ebbinghaus and Jost more than a century ago.