The present study investigated patterns of normative change in personality traits across the adult life span (19 through 74 years of age). We examined change in extraversion, agreeableness, conscientiousness, neuroticism, openness to experience and honesty-humility using data from the first 6 annual waves of the New Zealand Attitudes and Values Study (N = 10,416; 61.1% female, average age = 49.46). We present a cohort-sequential latent growth model assessing patterns of mean-level change due to both aging and cohort effects. Extraversion decreased as people aged, with the most pronounced declines occurring in young adulthood, and then again in old age. Agreeableness, indexed with a measure focusing on empathy, decreased in young adulthood and remained relatively unchanged thereafter. Conscientiousness increased among young adults then leveled off and remained fairly consistent for the rest of the adult life span. Neuroticism and openness to experience decreased as people aged. However, the models suggest that these latter effects may also be partially due to cohort differences, as older people showed lower levels of neuroticism and openness to experience more generally. Honesty-humility showed a pronounced and consistent increase across the adult life span. These analyses of large-scale longitudinal national probability panel data indicate that different dimensions of personality follow distinct developmental processes throughout adulthood. Our findings also highlight the importance of young adulthood (up to about the age of 30) in personality trait development, as well as continuing change throughout the adult life span.