Part of the Historical Census Projects at the University of Minnesota and funded in part by the National Science Foundation, the IPUMS consists of twenty-five high-precision samples of the American population drawn from thirteen federal censuses. Some of these samples have existed for years, and others were created specifically for this database. The twenty five samples span the censuses of 1850 to 1990 and provide a valuable source of quantitative information on long-term changes in the US population. This new version, IPUMS-98, contains new documentation, new data sets (1920, 1860 and 1870), and numerous new and revised variables.