Depression is one of the most common psychiatric disorders affecting societies all over the world. It is a period of illness in which the person experiences intense suffering, has thoughts of guilt and worthlessness, decreases energy and motivation, and has vegetative symptoms such as sleep and appetite problems. In addition, the person’s functionality deteriorates, and they have difficulty even continuing their daily life. One of the important points to be dealt with during this period is the risk of suicide. This situation is quite challenging for both physicians and patients. Classical antidepressant treatments, augmentation treatments, and Electroconvulsive Therapy maintain their place in the treatment of depression. New antidepressant agents and treatment methods that will strengthen our hands are being developed every day, such as Transcranial Magnetic Stimulation. While the Cognitive Behavioral Therapy approach continues to maintain its place, Schema therapy, which is a more integrative approach, provides an alternative. Depression treatment challenges many physicians in special groups, including pregnant and postpartum women (peripartum period), children and adolescents, and the geriatric population. This book consists of 5 main sections. In the first section, we aimed to provide general information on the definition, epidemiology, etiology, symptoms, diagnosis, classification, and prognosis of depression. The following sections of the book focus on the treatment of depression. In the second section, we talked about the current pharmacotherapy of depression. In the third section, biological treatment methods such as Electroconvulsive Therapy, Vagal Nerve Stimulation, Transcranial Magnetic Stimulation, and Deep Brain Stimulation were discussed. In the fourth section, information was given about the most commonly used psychotherapy methods in the treatment of depression, namely Cognitive Behavioral Therapy and Schema Therapy. In the last section, depression treatment in special groups such as pregnant and postpartum women (peripartum period), children and adolescents, and the geriatric population was discussed. The purpose of this book is to present current treatment approaches in addition to ancient approaches to depression treatment. We hope it will be beneficial to all our colleagues and other mental health professionals who are dedicated to their profession.