Recognizing that household structure is changing and that it varies among different race/ethnic groups and over time, the Census Bureau funded exploratory ethnographic research in the spring of 2000 to learn more about non-nuclear, or complex, households and to identify ways we might improve enumeration of them. This study identifies and describes complex households in selected ethnic groups in the United States, falling into the official Office of Management and Budget categories of African-American, American Indian and/or Alaska Native, Hispanic/Latino, Asian, and non-Hispanic white. The specific ethnic groups studied include Korean immigrants in Queens, New York, one location of the upcoming 2004 census site test (Kang 2000); Latino immigrants in central Virginia (Blumberg and Goerman 2000); African Americans in southeastern Virginia (Holmes and Amissah 2002); rural non-Hispanic whites in western New York (Hewner 2000); Navajo Indians on the Arizona reservation (Tongue 2000); and Inupiaq Eskimos, known as the Inupiat, in Alaska (Craver 2000). The project and report has three aims. The first is to explore the range and functioning of complex households within different ethnic groups. The second is to examine how well the response categories of the decennial relationship question capture the emerging diversity of household types in this country. The third aim has three components: a) to assess how well census methods, questions, relationship categories and household composition typologies describe the emerging diversity of household types, b) to suggest revisions to the relationship question and response categories for the 2010 census test cycle; and c) to call for new research.