Party politics at the European level dates back to the 1950s when the first Members of the Common Assembly, as the European Parliament (EP) was then known, decided to sit in groups according to political affinity rather than nationality. Over the years extra-parliamentary party federations have formally transformed themselves into European-level political parties, with further consolidation likely as a result of the Lisbon Treaty. Nonetheless, they remain less influential than the party Groups, which enjoy considerably more resources. Taking the Liberal family as its case study, this article provides an account of the evolution of party ties and party formation at European level. It argues that the origins of party political cooperation were ideological but that repeated institutional reform created pragmatic reasons for them to consolidate and to expand, and ultimately to seek power. It argues that Europarties and EP party groups may not be part of an inexorable trend towards European political parties that replicate the role of national parties. Rather they form part of complex patchwork of party cooperation and interaction, vertical and horizontal, where different types of cooperation are suitable for different forums.