The idea that mental disorders are brain disorders is widely shared among the major American institutions (e.g. the American Psychiatric Association, the National Institute of Mental Health), and is also a theoretical assumption of many nosological classifications and research projects, including the recent Research Domain Criteria project (RDoC). At the same time, this claim is constantly challenged by specialists. Addiction studies are a striking example: the neuroscientific, clinical, and philosophical literature questioning the brain disease model of addiction is extensive, and the debates are heated. In the context of broader theoretical discussions about the concept of brain disorder, a vast literature in psychiatry and philosophy exists, generally focusing on the differences and relationships between mental, neurological, and organic diseases. Although substantial, these discussions have not led to a satisfactory consensus description of the links between mental disorder and brain disorder. As its title suggests, it is this complicated issue that Anneli Jefferson, currently a lecturer at Cardiff University, tackles in her first monograph, Are Mental Disorders Brain Disorders? Her book aims to answer two questions: first, what is a brain disorder? And second, what is the relationship between mental disorders and brain disorders?