This chapter contains the theoretical framework the study in this book is based on. Embedded in institutional theory and building on four strands of literature—semi-presidentialism, public administration, political leadership, and foreign policy analysis—it highlights the role of institutions in facilitating successful policy-making. It outlines key concepts and findings from institutional theory before moving more specifically to the incentives that presidents and prime ministers have for engaging in intra-executive cooperation. The specific challenges related to leadership in foreign and security policy, including European Union affairs, are emphasized. The chapter identifies various intra-executive coordination mechanisms and puts forward a theoretical framework for the subsequent empirical chapters.