Memory is what defines who we are and who others are in our minds. It shapes our moral and intellectual personality, and the way we think and behave. Indeed, it would be impossible to live as one person, with an individual history or consciousness, without the memory threads that constantly link our present to our past and future. But why are memories so complex and mysterious? We remember things every instant, but how are memories formed? And why, if remembering is so ordinary, do our memories fail so often? What is happening in the brain when we recall a face, reconstruct the image of a place, or struggle to find an answer that we think we know? Does storage imply that memories are fixed in particular chunks of brain tissue, or is it a dynamic, biologically creative process that involves many different parts of the brain? How long do different memories last? What do genes have to do with memory? And, finally, are we the only creatures that remember and forget, and, if not, are there commonalties in the memories of different species? This is a fascinating work of popularisation that attempts to answer all these questions and more, deftly weaving the history of ideas about memory with cutting-edge science and psychology.