For decades the European Commission’s possible legislative influence has interested scholars of EU studies, yet few empirical studies on the determinants of the Commission’s influence exist. This paper analyses quantitative data on 60 EU proposals to show to which degree rather endogenous resources of the Commission, external conditions determined by the EU member states or institutional constraints determine the Commission’s influence on EU legislation. Modeling the Commission as an agent having resources and strategic options, I demonstrate that the Commission’s ability to defend the content of its original proposals is to a large extent dependent on its principals, the member states. Endogenous resources of the Commission such as expertise and experience influence only to a small extent the legislative success of the Commission. Thus, this study allows gaining a deeper understanding on the factors influencing the European Commission’s influence on legislative affairs.