This article examines how processes of aging, generational shifts, and changes over historical time periods shape differences in work values in the United States. Our analyses of data from the General Social Survey and the International Social Survey Program show that changes over historical time periods are most consistently responsible for differences in work values. In particular, during recent periods, Americans tend to place greater importance on jobs that provide security, high income, and opportunities for advancement; this is consistent with a narrative that these job rewards have become more difficult to attain recently and are thus more problematic for workers. Some differences in work values are also attributable to aging or life course processes, especially the greater importance placed on high income during the mid-life years when family responsibilities are generally greatest. By contrast, we find few differences in work values among members of different generations or cohorts. We also find that people from less advantaged social origins and those with greater labor market resources are more likely to value economic rewards. © 2018 by The American Academy of Political and Social Science.