Most of us think of memory as a fixed, unchanging substance that exists permanently in our mind and can be called upon at will. But research shows that this conception is far from the truth. We are constantly rewriting our memories and, in the process, creating ever new personal histories, illustrating that our memory operates in very complex and sometimes puzzling ways. This work explains why some memories can only be recalled in certain physiological states; why seemingly unimportant, small moments lurk in our memory for years for no apparent reason; and why some people have total recall of all that they read and see. It also shows how and why people who witness the same event recall it so differently and how we can often have vivid and detailed memories of events that never occurred.