Memory is a large topic, growing out of the fundamental fact that the experiences we have can modify the nervous system such that our mental life and our behaviour can be different than they were in the past. The study of memory ranges widely — from cellular and molecular questions about the nature of synaptic change to questions about what memory is: whether it is one thing or many, which brain systems support memory, and how those systems operate. We will consider in particular the structure and organization of memory with a focus on brain systems.