This commentary reviews recent demographic trends in immigration and intermarriage that contribute to the complexity of measuring race and ethnicity. The census question on ancestry is proposed as a possible model for what we might expect with the race question in the 2000 census and beyond. Through the use of ancestry data, changes in ethnic identification by individuals over the course of their lives, by generation, and according to census question directions are documented. It is pointed out that the once-rigid lines that divided European-origin groups from one another have increasingly blurred. All of these changes are posited as becoming more likely for groups we now define as "racial." While it is acknowledged that race and ethnicity will become increasingly difficult to measure as multiple racial identities become more common and more likely to be reported, it is argued that monitoring discrimination is crucial for the continued collection of such data.