The American Opportunity Study (AOS) is an initiative to produce linked restricted microdata files from the decennial censuses of 1960 through 1990. When combined with existing linkages between the censuses of 1940, 2000, 2010, the soon-to-be public 1950 census, and the future 2020 census, the AOS will provide the final component in a longitudinal data infrastructure that covers most of the U.S. population since 1940. Through enabling unprecedented analyses of the long-term causal effects of policy changes, this dataset will effectively revolutionize the country?s capacity for evidence-based policymaking and social science research.