Much attention has been given to generational differences in level and rate of age changes in the study of adult behavioral development. Much less work has been done on generational differences in personality development. This study examined cross-sectional and longitudinal data from the Test of Behavioral Rigidity administered to more than 3,000 subjects over the age range from 22 to 84 years. Data were analyzed from the behavioral flexibility, attitudinal flexibility, and social responsibility questionnaire scales, as well as from performance score measures indexing associational flexibility, instructional set flexibility, copying speed, and associational speed. Data on these scales were obtained for five samples examined 7 years apart (1956, 1963, 1970, 1977, and 1984). Within cohort data are available over 7, 14, 21, and 28 years respectively, allowing direct longitudinal estimates. These data permit analyses of cohort differences and rate of change within cohort over as long as 28 years. Results of the analyses confirm the presence of substantial generational differences, with generally only limited change over time within cohorts. The data suggest that there has been a substantial positive development toward more flexible personality styles, behaviors, and attitudes in successive generations over the past 70 years. (Three data tables and four figures are included.) (Author/NB)