The objective of this chapter is to carry out such an analysis. As the national parliaments are conceptualized as collective actors, the analysis is grounded in neo-institutional theories and their key assumptions are tested. Before that, the chapter reviews the role of parliaments within the democratic deficit debate and explains the mechanism that is used in order to involve national parliaments as actors of the EU political system. This section also comments on existing research dealing with the role of parliaments within the EU political system, paying particular attention to the work analysing national parliaments as a tool contributing to the better quality of EU democracy. In the following section, the hypotheses are presented in the context of neo-institutional theories. After that, the chapter analyses the collective actorness of EU national parliaments in the period of 2010–14 using their participation in the so-called Early Warning System (EWS) in order to find out whether parliaments succeeded in establishing an effective collective institution, which factors are shaping it and what their influence means for national parliaments’ contribution to EU democracy and legitimacy. As its main finding, the analysis reveals that national The chapter carries out an analysis of national parliaments as collective actor involved in EU decision making process. The analysis is grounded in neo-institutional theories and their key assumptions are tested. Before that, the chapter reviews the role of parliaments within the democratic deficit debate and explains the mechanism that is used in order to involve national parliaments as actors of the EU political system. This section also comments on existing research dealing with the role of parliaments within the EU political system, paying particular attention to the work analysing national parliaments as a tool contributing to the better quality of EU democracy. In the following section, the hypotheses are presented in the context of neo-institutional theories. After that, the chapter analyses the collective actorness of EU national parliaments in the period of 2010–14 using their participation in the so-called Early Warning System (EWS) in order to find out whether parliaments succeeded in establishing an effective collective institution, which factors are shaping it and what their influence means for national parliaments’ contribution to EU democracy and legitimacy. As its main finding, the analysis reveals that national parliaments failed in the period 2010–14 to establish an effective collective institution.