US cities bordering Mexico are unique not only because their geography and history connect them to contrasting social, economic, and institutional systems across the border, but because they exist in a policy and political space of exceptionality. Within a 100-mile zone from the international boundary, US cities and their inhabitants are subject to policies of surveillance, scrutiny, and suspicion, on the one hand, while seemingly divergent policies animate cross-border trade, tourism, outsourcing, and integration, on the other. This chapter explores the implications of bordering for socio-spatial integration and differentiation of US urban places abutting Mexico. In particular, we examine the effect of bordering on the socio-spatial structuration of micropolitan Nogales (Arizona) and the planning and governance of metropolitan San Diego (California). We argue that, even when the structuration of urban space reflects a number of complex and large-scale historical, cultural, and economic factors, it also offers an indication of the local response to the intensification of rebordering/debordering dynamics.