Book excerpt: The usefulness of the U.S. decennial census depends critically on the accuracy with which individual people are counted in specific housing units, at precise geographic locations. The 2000 and other recent censuses have relied on a set of residence rules to craft instructions on the census questionnaire in order to guide respondents to identify their correct "usual residence." Determining the proper place to count such groups as college students, prisoners, and military personnel has always been complicated and controversial; major societal trends such as placement of children in shared custody arrangements and the prevalence of "snowbird" and "sunbird" populations who regularly move to favorable climates further make it difficult to specify ties to one household and one place. Once, Only Once, and in the Right Place reviews the evolution of current residence rules and the way residence concepts are presented to respondents. It proposes major changes to the basic approach of collecting residence information and suggests a program of research to improve the 2010 and future censuses.