This chapter presents a critical overview of the literature based on the roughly 60 principal-agent (PA) articles published in the main journals in the field since 2000. Over the past 20 years analysts of policy-making in the European Union (EU) have made extensive use of PA theory. The first, and probably most important warning against relying too much on PA when analyzing EU policy-making came from Majone, one of the earliest proponents of the theory. The PA literature has yielded important insights on the EU policy-making processes. PA theory may have become a victim of its own success. Although such an approach simplifies the appointment rules, it certainly offers a clearly understandable application of PA theory. All other studies analyze the delegation of powers carried out either by one collective principal or by multiple and collective principals – such as member states, the Commission, and the European Parliament.