In the present research, we examined the effects of age, cohort, and time of measurement on well-being across adulthood. Cross-sectional and longitudinal analyses of two independent samples-one with more than 10,000 repeated assessments across 30 years (mean assessments per participant = 4.44, SD = 3.47) and one with nationally representative data-suggested that well-being declines with age. This decline, however, reversed when we controlled for birth cohort. That is, once we accounted for the fact that older cohorts had lower levels of well-being, all cohorts increased in well-being with age relative to their own baseline. Participants tested more recently had higher well-being, but time of measurement, unlike cohort, did not change the shape of the trajectory. Although well-being increased with age for everyone, cohorts that lived through the economic challenges of the early 20th century had lower well-being than those born during more prosperous times. © The Author(s) 2013.