Obsessive compulsive disorder is currently the subject of considerable research, since recent epidemiological studies have suggested that the condition is more prevalent than was originally believed. This book offers a critical discussion of the most important theories that have been put forward to explain this disorder. The book includes behavioural/learning accounts (and cognitive-behavioural supplements of these), accounts based on Pavlovian personality theories (such as those by Eysenck, Gray, and Claridge), Pierre Janet’s account, cybernetic approaches, psychodynamic approaches, Reed’s ‘cognitive-structural’ account, and biological approaches. Therapeutic approaches to the disorder are also considered, insofar as they are relevant to these theories. This book is unique in both the comprehensiveness and the depth of its coverage of theories of OCD. It also offers an entirely new approach to the definition of the disorder.