In this book, obsessive-compulsive disorder (OCD) is examined with a neuropsychological and biological approach. In this regard, attention has been paid to bring the latest researches and studies in the field of genetics, neurotransmitters, nervous-brain system in causing obsessive-compulsive disorder in this work. Animal models and pharmacology of obsessive-compulsive disorder have also been studied. Since most of these researches and studies, directly or indirectly, have investigated the role of the complex and mysterious system of the human brain in creating OCD, the title of this work was chosen as “Brain and Obsession”. This book is especially useful and valuable for researchers and students of psychiatry and psychology.