Mental disorders, also called mental illnesses, refer to conditions that affect the thinking, feeling, mood, and behavior of a person. Such disorders may affect a person occasionally or may be chronic. Such disorders can potentially impact a person's ability to perform their functions normally. There are various types of mental disorders such as anxiety disorders (panic disorder, obsessive-compulsive disorder, and phobias), depression, bipolar disorder, mood disorders, eating disorders, personality disorders, post-traumatic stress disorder (PTSD), and psychotic disorders. Depression is a serious mood disorder that that negatively affects how a person feels, thinks, and acts. There are multiple causes of mental disorders and depression such as genetics, family history, life experiences, stress, abusive past, traumatic brain injury (TBI), cancer, etc. Physical examination, laboratory tests, and psychological evaluation are used to diagnose mental disorders. The treatment of mental disorders and depression depends on the type of disorder and its severity. This book unravels the recent studies on mental disorders and depression. It will serve as a valuable source of reference for graduate and post graduate students.