Depression is a common, serious, and deadly illness. Recent evidence suggests that it is underrecognized by physicians and, even when diagnosed, treated insufficiently ("too little too late"). Modern antidepressant drugs are highly effective for most patients with more serious (nonpsychotic) depressions, whereas newer psychosocial approaches can benefit patients on the milder end of the spectrum. Many patients improve with combined pharmacotherapy and psychotherapy. What causes the depressive diathesis and what triggers depressive episodes remain enigmas despite centuries of observations and decades of scientific research. Presumably, genetics and early life experiences contribute to the diathesis. Possible triggers of episodes include changes in internal chemistry, stress and loss, and the coming of the winter solstice. Medical illnesses and the drugs used to treat them may also cause depression, particularly in predisposed individuals. Typical lists of possible "organic" causes resemble tables of contents from internal medicine textbooks. A multitude of factors upsetting the