Memory is vital to forming a person’s identity and providing the stable sense of reality we need to function in daily life. Despite memory’s fundamental importance, its basis in the brain remains largely mysterious. Attempts to develop computer models of the brain show that memory is far more complex - and often counter-intuitive - than any system yet devised by software designers. A memory is a far cry from the information stored on a hard drive or in the Cloud: it can not only fade and disappear, but be falsified. Recently, scientists have begun to probe for memory’s basis in the brain on a cellular level, using tools such as optogenetics to manipulate neural circuits in living animals. Despite rapid progress, they are still far from grasping the neuronal processes by which a fully-fledged memory is formed, stored, and retrieved. It’s easy to take memory for granted. Only when it fails – because of diseases such as Alzheimer’s, a head injury, or other brain insults – do we appreciate the myriad complex components that constantly have to be coordinated to sustain it. This page provides an overview of important contributions to memory research ranging from the molecular basis of learning, to the pathology of neurodegenerative diseases.