Abstract: A prevailing notion in memory research is that the persistence of a given memory depends on the stability of its coding by the neurons that were active during learning. Recent studies revealed that hippocampal place codes and cortical sensory codes gradually change (or drift) over time, calling into question the notion that stable neural codes underlie stable memories. I will present results from experiments in which we used optical imaging to longitudinally study hippocampal neural codes for long-term spatial memory. Our results suggest that spatial memory content is reliably preserved over weeks without relying on the long-term stability of hippocampal representations. I will discuss how these surprising findings relate to current theories in memory research.