This panel examines the lives of residents throughout the U.S.-Mexico borderlands from the late nineteenth century through the twentieth century. It considers the ways in which the international boundary functioned sometimes as a barrier and sometimes a gateway between the two countries, often simultaneously. Together, the panelists demonstrate how transfrontier landscapes challenged the very salience of the arbitrary border. Examining the transborder domesticity of women of Mexican descent in New Mexico and Chihuahua during the late nineteenth century, Katherine Massoth challenges the idea of the U.S.-Mexico border as a barrier dividing families. She shows that domesticity allowed some women to sustain kin relationships and maintain cultural and economic ties across the international boundary during these years. C.J. Alvarez examines the lives of border dwellers in the binational Chihuahuan Desert. Conceptualizing this desert as a single ecoregion, he explores the notion of the international boundary that intersects it as an “abstraction.” Alina Mendez looks at the ways in which the Bracero Program expanded possibilities for labor and migration across the U.S.-Mexico Border and shows how migrant workers and employers viewed the international boundary as an obstacle to be eliminated with the cooperation of the state. Kevan Malone examines rapid urbanization in the Tijuana-San Diego borderlands after World War II, considering what it means that the two cities were growing increasingly interconnected during a period in which the United States was erecting barriers between them. He highlights the displacement of poorer borderland residents by urban development projects on both sides of the line. Considering transborder ecologies, development, and communities, this panel moves beyond the idea of the border as simply a division or barrier. Together the papers reveal how the U.S.-Mexico border has, at various points, served different roles in the regional landscape, depending on the actors and governments involved. The making and remaking of the US-Mexico border occurred at the local, regional, and national level as individuals, organizations, and public and private institutions left their mark on the landscape and its peoples. As policymakers continue debating the further militarization of the United States’ southern border, this panel offers fresh historical perspectives for thinking about this contested region.