In relation to the first edition of the bookpublished in 2009, this second edition, brings significantadvances, specifically regarding new terminology andin the classification of disorders, today’s terms replaceolder ones or are included side by side, and new materialpublished since then is coved.The book is organized into four parts: clinicalaspects, experimental aspects, theoretical aspects, andtreatment of depression. Part I describes the definition,symptoms, course and prognosis of depression, as wellas ratings of mood disorders, depression, psychoticversus nonpsychotic depression, bipolar disorders,involutional depression and schizoaffective disorder.Part II reports biological and psychological studies ofdepression, including psychoanalytic theory tests. PartIII investigates theories of depression, cognition andpsychopathology and the development of depression.Part IV describes the main treatments for depression,including the somatic therapies, psychotherapy and theassessment of treatments for depression: randomcontrolled trials.Part I presents the questions about depressionthat are present throughout human history. Even thoughit has been recognized as a clinical syndrome for overtwo thousand years, an entirely satisfactory explanationof its intriguing and paradoxical features has not beenfound. There are few psychiatric syndromes in whichthe clinical definitions are so constant throughoutconsecutive periods of history. The nature and etiologyof depression are subject to different concepts. Somescholars ensure that depression is a psychogenicdisorder, while others claim that it is caused by organicfactors. A third group believes in two different types ofdepression: one psychogenic and the other organic.Schizophrenia and depression constitute the firstand second most common diagnoses, respectively, foradmissions to psychiatric hospitals in the United States,and the prevalence of depression outside psychiatrichospitals is evaluated as being five times that ofschizophrenia. According to the fourth edition of theDiagnostic and Statistical Manual of Mental Disorders(DSM-IV) of the American Psychiatric Association (APA),the likelihood of developing major depressive disorderduring life is from 12% to 15% for men and from 10% to25% for women. Major depressive disorder is the mainreason for disability in strengthened market economiesaround the world.In