This chapter reveals the ambiguous attitude towards the EPPO by the European Parliament, a key actor of supranationalisation, EU budgetary control, and the protection of the rule of law which nonetheless wielded little influence during the EPPO negotiations. The chapter interprets the varying levels of parliamentary involvement with reference to opportunities and constraints at the institutional, individual, and ideational level. The EP’s contribution to the overall success of the project highlights the importance of inter-institutional alliances, as well as the potential for parliamentary power despite unfavourable institutional rules. But the insignificance of the EP in defining the exact modalities of the EPPO also demonstrates the strict limits within which the EP acts as a go-to body for accountability and democratic legitimacy today. Finally, the chapter reveals that, following the adoption of the EPPO Regulation, the EP has re-emerged as a guardian of the EPPO’s independence and action capacity. The chapter, thus, concludes that parliamentary dynamics only punctually shaped the emergence and implementation of the EPPO.