Abstract
One of the challenges of a decentralized system like Spain is ensuring intergovernmental cooperation, thus promoting an effective multi-level environmental governance. This article attempts to shed some light on the existing forms of cooperation between State and Autonomous Communities in the environmental field. Drawing on extensive data collection, empirical findings show that current intergovernmental cooperation (mainly through the mechanisms of the Environmental Sectorial Conference and Bilateral Commissions), even though not negligible, is still fragile in the event of shared competence that goes beyond the common implementation of administrative activities. Thus the role of the Constitutional Court is likely to be pre-eminent with regard to the exercise of shared environmental competences.