Depression is a major public health problem associated with increased functional disability and mortality. The annual economic consequences of depression were estimated at 83 billion dollars in the United States in 2000  and 118 billion euro in Europe in 2004 .
The epidemiology, pathogenesis, and neurobiology of depression in adults are reviewed here. The clinical features, diagnosis, treatment, and prognosis of depression are discussed separately.
Prevalence — Depression is highly prevalent throughout the world and the prevalence appears to be increasing. Surveys of adults living in the community in 10 countries (Brazil, Canada, Chile, Czech Republic, Germany, Japan, Mexico, Netherlands, Turkey, and the United States) found that the lifetime prevalence of major depression varied from 3 percent in Japan to 17 percent in the United States, with most rates in the range of 8 to 12 percent .
The prevalence of depressive disorders is similar across Western nations and lower in Far Eastern countries . This may reflect true variation in the determinants of depression due to cultural or genetic factors, sample selection biases, and problems with the cross-cultural portability of DSM-IV diagnostic criteria [4,5].