This article suggests a thought and analysis the mismatch between the implementation of the State of Autonomies and the scarce cooperation and collaboration between Autonomous Communities in the face of a set of contemporary urban and territorial phenomena that clearly goes beyond regional political-administrative limits and in turn define new territorial areas of intermediate scale. First, the paper contextualises the fit of interregional cooperation in the Spanish legislation and points out the possible factors conditioning the scarce use of this instrument (collaboration agreements and cooperation agreements between Autonomous Communities). Second, the initiatives and files collected in the Senate database are analysed and characterised. This analysis evidences the insufficient degree of interregional cooperation. The paper ends with a discussion in regard to the importance of this instrument for responding to common problems and establishing development projects in cross-border territories. © Instituto Universitario de Urbanística de la Universidad de Valladolid. All rights reserved.