A group of conditions where a disturbance in the person's mood is the primary feature is known as a mood disorder. It falls under the basic groups of elevated moods, such as mania or hypomania. Major depressive disorder and bipolar disorder are the two primary types of mood disorders. A major depressive disorder is a condition where a person has more than one major depressive episode. Individuals with a major depressive disorder are at high risk of committing suicide. Bipolar disorder is an unstable emotional condition characterized by cycles of abnormal mood, mania and depression. A mood disorder can also be substance-induced, alcohol-induced or can occur due to other medical conditions. It can be treated with the help of therapy and medications. The diagnosis, prevention, and treatment of mood disorder fall under the domain of psychiatry. This book unravels the recent studies related to mood disorders. It also includes some of the vital pieces of work being conducted across the world, on various topics related to such disorders. This book is appropriate for students seeking detailed information in this area as well as for experts.