Droughts are recurrent climatic hazards that cause major environmental, economic and social impacts, and increase the conflict potential between countries sharing transboundary river basins. The shared river basins of the Iberian Peninsula, and the Guadiana in particular, are of major significance for Mediterranean Europe, as examples of basins marked by aridity, water scarcity, and drought risk. A political agreement (the Albufeira Convention) regulates water issues between Portugal and Spain but an exception regime is applied under drought conditions, and the Convention looses its effectiveness. The two countries have different planning and management policies to tackle droughts, based on distinctive administrative and socio-economic structures. This paper analyses each country's framework, and assesses the level of cooperation and compliance with the basic pillars of transboundary water governance, identifying the potential and constraints for shared and effective transboundary drought planning and management. The analysis conducted shows how both countries fail to identify common benefits and goals, based on a shared process of public participation (which still does not exist). The paper concludes that, before aiming for a shared or joint planning process, both countries need to incorporate adaptive and precautionary management procedures into their planning systems and cooperation structures.