This article discusses the second edition of a book on depression, which includes new terminology and classifications. The book is divided into four parts: clinical aspects, experimental aspects, theoretical aspects, and treatment of depression. Part I describes the definition, symptoms, course, and prognosis of depression, as well as mood disorders, psychotic versus nonpsychotic depression, bipolar disorders, involutional depression, and schizoaffective disorder. Part II covers biological and psychological studies of depression, including psychoanalytic theory tests. Part III investigates theories of depression, cognition, psychopathology, and the development of depression. Part IV describes the main treatments for depression, including somatic therapies, psychotherapy, and the assessment of treatments through random controlled trials. The article highlights the prevalence of depression, noting that it is the main cause of disability in strong market economies. It describes the symptoms of depression, including emotional, cognitive, and physical manifestations. It also discusses the course and prognosis of depression, as well as classifications of mood disorders. The article addresses the distinction between non-psychotic and psychotic depression, and the challenges in classifying involutional depression. It also notes the lack of studies on schizoaffective disorder. Part II of the book discusses the experimental aspects of depression, highlighting the limited basic knowledge on the biological substrate of depression. It also notes the controversy surrounding the neurobiology of suicidal behavior. Part III presents various theories of depression, including behavioral, cognitive, evolutionary, psychoanalytic, and biochemical theories. It also discusses the primary triad of depression and the relationship between stress and depression. Part IV describes the main somatic therapies, current pharmacotherapy, and psychotherapy. It emphasizes cognitive therapy as an effective treatment for depression, with data showing that patients treated with psychological interventions had a lower relapse rate compared to those treated with pharmacotherapy alone. The book also includes an appendix on the scoring of negative dreams. The book is a valuable resource for psychology and psychiatry professionals, providing a comprehensive overview of depression and its treatment. It also highlights the need for further research on depression and the lack of consensus among systematic studies.This article discusses the second edition of a book on depression, which includes new terminology and classifications. The book is divided into four parts: clinical aspects, experimental aspects, theoretical aspects, and treatment of depression. Part I describes the definition, symptoms, course, and prognosis of depression, as well as mood disorders, psychotic versus nonpsychotic depression, bipolar disorders, involutional depression, and schizoaffective disorder. Part II covers biological and psychological studies of depression, including psychoanalytic theory tests. Part III investigates theories of depression, cognition, psychopathology, and the development of depression. Part IV describes the main treatments for depression, including somatic therapies, psychotherapy, and the assessment of treatments through random controlled trials. The article highlights the prevalence of depression, noting that it is the main cause of disability in strong market economies. It describes the symptoms of depression, including emotional, cognitive, and physical manifestations. It also discusses the course and prognosis of depression, as well as classifications of mood disorders. The article addresses the distinction between non-psychotic and psychotic depression, and the challenges in classifying involutional depression. It also notes the lack of studies on schizoaffective disorder. Part II of the book discusses the experimental aspects of depression, highlighting the limited basic knowledge on the biological substrate of depression. It also notes the controversy surrounding the neurobiology of suicidal behavior. Part III presents various theories of depression, including behavioral, cognitive, evolutionary, psychoanalytic, and biochemical theories. It also discusses the primary triad of depression and the relationship between stress and depression. Part IV describes the main somatic therapies, current pharmacotherapy, and psychotherapy. It emphasizes cognitive therapy as an effective treatment for depression, with data showing that patients treated with psychological interventions had a lower relapse rate compared to those treated with pharmacotherapy alone. The book also includes an appendix on the scoring of negative dreams. The book is a valuable resource for psychology and psychiatry professionals, providing a comprehensive overview of depression and its treatment. It also highlights the need for further research on depression and the lack of consensus among systematic studies.