First published online: 15 October 2019The aim of this chapter is to present the evolution and strengthening of the European Parliament Political Groups and European Political Parties from a comparative perspective. The specific focus is on the relation between the two faces of the EU political system. Despite the number of studies on the organizational aspects of the European Parliament Political Groups (EPPGs) and the European Political Parties (EuPPs), the literature is still scarce for what concerns the relationship between the two organizations. This chapter gives empirical evidence to the oft-repeated (yet seldom demonstrated) predominance of the groups in respect to their corresponding European parties. In fact, this is true from a m...