We present evidence that psychological well-being is U-shaped through life. A difficulty with research on this issue is that there are likely to be omitted cohort effects (earlier generations may have been born in, say, particularly good or bad times). First, using data on 500,000 randomly sampled Americans and West Europeans, the paper designs a test that can control for cohort effects. Holding other factors constant, we show that a typical individual's happiness reaches its minimum - on both sides of the Atlantic and for both males and females - in middle age. Second, evidence is provided for the existence of a similar U-shape through the life-course in East European, Latin American and Asian nations. Third, a U-shape in age is found in separate well-being regression equations in 72 developed and developing nations. Fourth, using measures that are closer to psychiatric scores, we document a comparable well-being curve across the life cycle in 2 other data sets (1) in GHQ-N6 mental health levels among a sample of 16,000 Europeans, and (2) in reported depression-and-anxiety levels among 1 million UK citizens. Fifth, we discuss some apparent exceptions, particularly in developing nations, to the U-shape. Sixth, we note that American male birth-cohorts seem to have become progressively less content with their lives. Our results are based on regression equations in which other influences, such as demographic variables and income, are held constant.