The provisional application of treaties has become a common feature in contemporary treaty practice, and international organizations have been increasingly relying on this tool to ensure the execution of international agreements. However, the provisional application of treaties to which international organizations are party entails complex le gal questions regarding the impact of internal rules of international organizations on the legal regime of the implementation of such tr eaties. Against this background, the author evaluates the practice of the European Union in provisionally applying treaties at the crossroad of international law and internal rules of the organization. To this end, the article assesses whether and to what extent the internal rules of the European Union might affect the e xecution of provisionally applied treaties and the validity of the agreements providing for their provisional application.