How much do people's personalities change or remain stable from high school to retirement? To address these questions, we used a large U.S. sample (N = 1,795) that assessed people's personality traits in adolescence and 50 years later. We also used 2 independent samples, 1 cross-sectional and 1 short-term longitudinal (N = 3,934 and N = 38, respectively), to validate the personality scales and estimate measurement error. This was the first study to test personality stability/change over a 50-year time span in which the same data source was tapped (i.e., self-report). This allowed us to use 4 different methods (rank-order stability, mean-level change, individual-level change, and profile stability) answering different developmental questions. We also systematically tested gender differences. We found that the average rank-order stability was .31 (corrected for measurement error) and .23 (uncorrected). The average mean-level change was half of a standard deviation across personality traits, and the pattern of change showed maturation. Individual-level change also supported maturation, with 20% to 60% of the people showing reliable change within each trait. We tested 3 aspects of personality profile stability, and found that overall personality profile stability was .37, distinctive profile stability was .17, and profile normativeness was .51 at baseline and .62 at the follow-up. Gender played little role in personality development across the life span. Our findings suggest that personality has a stable component across the life span, both at the trait level and at the profile level, and that personality is also malleable and people mature as they age. (PsycINFO Database Record (c) 2019 APA, all rights reserved).