Depression, often referred to as the “common cold of psychopathology”, is among the most prevalent psychiatric conditions, yet it remains challenging to understand and treat. Experience such as the difficulty of continuing on with one’s typical routine, desires, and goals that differentiate more normal experiences of sadness and malaise from syndromes of depression drive people to seek treatment for these conditions. This book provides an overview of all aspects of unipolar and bipolar depressive disorders, including their presentation, course, impact on functioning, etiology, and treatment. It integrates recent research on risk factors for these conditions and biological underpinnings of depression and mania alongside well-established observations regarding the phenomenology and correlates of these conditions. The book explicitly integrates models of depression such as the diathesis-stress model and vulnerability model, across childhood, adolescence, and adulthood. The book shows how such major psychology disciplines as clinical, developmental, evolutionary, personality, and behavioral neuroscience shed light on the causes, risk factors, and treatment options for the full spectrum of depressive disorders. It describes what is known about the kinds of stress that seem to be most relevant to depressive disorders; how this stress may exert its effects; and other factors that may help to explain individual differences in the stress-depression relationship. Cultural and gender as variables are examined as is depression across the lifespan. In addition, the book clarifies common misconceptions about depression and mood disorders, and considers how the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) affects diagnostic practice.