acting [together] in accordance with the ordinary legislative procedure, may adopt detailed rules for the multilateral surveillance procedure'. With the outbreak of the economic and financial crisis, the EP made immediate use of its new powers. The reform of the Stability and Growth Pact (SGP) was negotiated under the ordinary legislative procedure (OLP) and, between September 2010 and February 2013, the EP and the Council established new rules for budgetary surveillance and macroeconomic coordination. With the approval of the two legislative packages known as the Six-Pack and the Two-Pack, for the first time the EP had the opportunity to shape the rules of the EMU.The literature has provided very different assessments of the role of the EP in the reform of the EMU. On the one hand, the EP has traditionally not shied away from using its powers as a colegislator (Corbett et al., 2016); with its new legislative powers, several scholars observed that the EP's impact has indeed been significant (Fasone, 2013;Héritier and Schoeller, 2015;Laffan and Schlosser, 2016). Even advocates of the 'new intergovernmentalism' recognise that the Six-Pack and the Two-Pack are an exception to their story (Fabbrini, 2013). On the other hand, other scholars noted that the EP was not very successful in pushing its preferences through, particularly on economic issues (Bressanelli and Chelotti, 2016;O'Keeffe, Salines and Wieczorek, 2016).This article presents an in-depth study of the influence of the EP in the Six-Pack and the Two-Pack.It has both descriptive and explanatory purposes. Descriptively, it aims to provide a systematic map of the negotiations focusing on the key controversies -i.e. important issues where the actors have different positions (Thomson, 2011, p. 29). To assess the EP's influence, we compare its position before starting the negotiations with the Council to the initial legislative proposals and the final legislative output. i This is complemented by an account of the genesis of the two packages. We anticipate here that the EP's influence has been modest at best. In the second part of the paper, we 2 explain this puzzling finding. Relying on rational and sociological institutionalism, we show that the more favourable BATNA of the Council could explain the outcome of the Two-Pack, and a norm of responsibility triggered by the crisis could account for the limited impact of the EP on the Six-Pack. Yet, we are not fully satisfied by the extant explanations, and advance a new, additional hypothesis. We suggest that in policy areas close to 'core state powers' (Genschel and Jachtenfuchs, 2013), like budgetary surveillance, the Member States still play a primary role, and the EP finds itself acting within the boundaries that they define. Our policy-based explanation contends that the EMU -and, possibly, other policies close to core state powers -have their own dynamics, where the Member States are still the 'masters', and the EP has a more subordinate position. While we do not completely dismiss the importance of the f...