In 1997, the US Government revised its standards for the collection of data on race. Previous US government practice dating back to the first US Census in 1790 forced people into mutually exclusive categories. The new policy allows people to identify themselves as being of more than one race. The 2000 Census is the first major national data collection exercise to use this new system and its results will reveal both the promise and the perils of the new system. On the positive side, the new scheme allows people who think of themselves as 'mixed' to be counted as such in official data. However, multiple race responses complicate efforts to count minority populations eligible for civil protection and voting rights laws. Furthermore, the new systems pose new opportunities and challenges for social scientists concerned with the measurement of ethnic and racial inequality. The paper ends with a discussion of the implications of the new rules for the imagination of America's ethno-racial future through population projections.