Summary is underdiagnosed and often inadequately treated. The disorder is a major cause of human suffering and social dysfunction and a significant cause of death. Studies conducted during the past two decades have shed new light on almost every aspect of this disorder—its biology, psychology, etiology, course and treatment. As a result of these researches there are several effective therapies available, including psychotherapy, specific antidepressant medications and electroconvulsive therapy. With proper diagnosis and appropriate treatment choice, up to 85% of patients will respond favorably to treatment. This review has attempted to present an overview of depression that will help the physician to recognize the disorder, even in its more obscure forms, and enable him to plan an effective treatment.