Along the U.S.-Mexico frontier, where border crossings are a daily occurrence for many people, reinforcing borders is also a common activity. Not only does the U.S. Border Patrol strive to "hold the line" against illegal immigrants, but many residents on both sides of the border seek to define and bound themselves apart from groups they perceive as "others." This pathfinding ethnography charts the social categories, metaphors, and narratives that inhabitants of El Paso and Ciudad Juárez use to define their group identity and distinguish themselves from "others." Pablo Vila draws on over 200 group interviews with more than 900 area residents to describe how Mexican nationals, Mexican immigrants, Mexican Americans, African Americans, and Anglos make sense of themselves and perceive their differences from others. This research uncovers the regionalism by which many northern Mexicans construct their sense of identity, the nationalism that often divides Mexican Americans from Mexican nationals, and the role of ethnicity in setting boundaries among Anglos, Mexicans, and African Americans. Vila also looks at how gender, age, religion, and class intertwine with these factors. He concludes with fascinating excerpts from re-interviews with several informants, who modified their views of other groups when confronted by the author with the narrative character of their identities.