The role and impact of institutions on policy-making have been receiving a lot of attention in the academic literature on the European Union (EU). The current special issue aims to contribute to this broader institutionalist debate in the EU literature by paying attention to institutional dynamics within and across EU institutions and different levels of governance. In this quest, it feeds into the broader political and academic debate on (changing) institutional balance and policy coherence. The contributions to this special issue reflect that a wide range of institutional mechanisms for intra-and inter-institutional cooperation have been developed. Most importantly, the contributions allow us to get a better insight into the factors that explain the success or failure of the cooperation. This introduction to the special issue provides the backdrop for the contributions and an overview of the individual articles.