Inter-municipal cooperation is one of the most important options for sustainable and balanced territorial planning and its lines of approach and level of effectiveness evidently face significant challenges when relations correspond to cross-border areas. The creation of the European Groupings of Territorial Corporation in 2006 as a Community concept specifically applied to territorial cooperation brings in a new perspective of unquestionable strategic interest and one that takes on particular relevance through the so-called Duero-Douro along a critical sector of the Spanish-Portuguese border.