The European University Initiative (EUI) -- launched by the European Commission in 2018 has been received with considerable interest from higher education institutions in Europe with hundreds of institutions forming new alliances. While the EUI-initiative in many ways is a continuation of a long history of collaboration across national borders in Europe, the initiative also contains novel elements -- not least with respect to the institutional commitments the new alliances are based on. This paper offers new insights into the alliance formation process, and the profiles of European university alliances. Based on a series of qualitative interviews with key persons at alliance level, our findings demonstrate quite complex alliance formation processes where both collective and individual networks of institutions were activated, and where different path-dependencies shaped the membership of the alliances.