A comprehensive and up-to-date review of obessionality which integrates a full range of research findings. The main aim of the book is to consider cognition, in the broadest sense, within the context of OCD. Chapters cover the historical development of OCD and its biological data; assessment; phenomenology - including emphasis on cognitive writings which link the observations of Freud with contemporary theories; neuropsychology; cognitive behavioral treatment; and cognition and brain state.