This paper is based on an ethnographic study carried out in the towns of Alcoutim (Algarve, Portugal) and Sanlúcar de Guadiana (Andalusia, Spain), both located on Guadiana River, which at these points constitutes the Portuguese-Spanish border. We study cross-border social relations and the role of state powers, which have historically defined the border through their strategies. Our analysis demonstrates that the actions of the respective public administrations have influenced the way of life at the local level as a result of the absence of significant cross-border cooperation initiatives and the predominant climate of mistrust, which have impacted the capacity of local communities to negotiate and establish permanent links. © 2022, Universitat Autonoma de Barcelona. All rights reserved.