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 Juarez use to define their group identity and distinguish themselves from "others." Pablo Vila draws on...