This chapter describes the groundwater management policy implemented in the Poitou marshes, a 100 000 ha wetland located on the Atlantic coast in Western France. Similarly, to other French basins, irrigated agriculture has rapidly developed since the 1980's, mainly based on groundwater exploitation. Clear signs of groundwater overexploitation appeared in 1992-95, with the intrusion of brackish water in the aquifer. Because of the overexploitation, ecosystems were severely affected and the French Government was sued by the European Commission for non-compliance with the Bird Directive (1999). The chapter describes the progressive implementation of a groundwater management policy aiming at ensuring the long-term sustainability of an emblematic groundwater dependent wetland. To do so, the State imposed a very significant reduction in historical water entitlements. This case study illustrates the difficulties encountered in implementing this reduction, in a context of extreme competition between economic uses (agriculture, urban and touristic) and environmental objectives. The case study also reports on the complexity of developing an integrated management plan in basins where groundwater, rivers, wetlands and canals are highly interdependent. It highlights the importance of a (shared) knowledge on water resource and uses, of involving stakeholders in the different steps, and of trying to share scarcity in an equitable way.