Media often portrays European Union (EU) decision-making as a battleground for national governments that defend the interests of their member states. Yet even the most powerful individuals, such as the German chancellor, the French president, or the Commission president, are party politicians. At the same time the consistent empowerment of the European Parliament (EP) means that the party groups of European-level “Europarties”—political parties at European level—are in a key position to shape EU legislation. The Parliament has also become more directly involved in the appointment of the Commission, with the results of EP elections thus influencing the composition of the Commission.

Examining the “partyness” of European integration, this article argues that scholarly understanding of the role of parties in the EU political system has taken great strides forward since the turn of the millennium. This applies especially to the EP party groups, with research focusing particularly on voting patterns in the plenary. This body of work has become considerably more sophisticated and detailed over the years; it shows that the main EP groups do achieve even surprisingly high levels of cohesion and that the left–right dimension is the primary axis of contestation in the chamber. It nonetheless also emphasizes the continuing relevance of national parties that control candidate selection in EP elections. Considering that most votes in the Parliament are based on cooperation between the two largest groups, the center-right European People’s Party (EPP) and the center-left Party of the European Socialists (PES), future research should analyze in more detail how these groups build compromises.

Actual Europarties, however, remain relatively unexplored. Case studies of treaty reforms or particular policy sectors reveal how individual Europarties have often wielded decisive influence on key integration decisions or key appointments to EU institutions. The Europarty meetings held in conjunction with European Council summits are particularly important in this respect. The regular, day-to-day activities of Europarties deserve more attention, both regarding decision-making and vertical links between national parties and their Europarties. Overall, it is probably more accurate to characterize Europarties as networks of like-minded national parties or as loose federations of member parties, especially when compared with the often centralized and strongly disciplined parties found in the member states.