Book excerpt: Most of us have been perplexed by a strange sense of familiarity when doing something for the first time. We feel that we have been here before, or done this before, but know for sure that this is impossible. In fact, according to numerous surveys, about two-thirds of us have experienced déjà vu at least once, and most of us have had multiple experiences. There are a number of credible scientific interpretations of déjà vu, and this book summarizes the broad range of published work from philosophy, religion, neurology, sociology, memory, perception, psychopathology, and psychopharmacology. This book also includes discussion of cognitive functioning in retrieval and familiarity, neuronal transmission, and double perception during the déjà vu experience.