Obsessive-compulsive disorder (OCD) is a common mental disorder that may seriously affect quality of life. Recently proposed treatment strategies (e.g. deep brain stimulation or neurofeedback) aim to target several levels of the underlying dysfunctional fronto-striatal circuits and thus critically depend on good knowledge of neurobiological basis of the disorder. This book provides an overview of the current literature related to OCD and summarizes the results of five original studies of the author conceived 1) to explore anatomical correlates of OCD, 2) to verify their functional relevance and specificity in EEG studies, and 3) to test the utility of the findings in neurofeedback treatment. The results support the current opinion that abnormalities in OCD exceed the traditional orbitofronto-striatal loop and include more widely distributed brain regions. Central role of the anterior cingulate across our studies as well as increased amount of low-frequency activity in OCD suggest the involvement of the reward system and offer a new view of OCD as a salience network-related disorder. This publication may be useful especially to professionals and students in the field.