Any democratic regime needs an active and performative party system. Political parties act as intermediaries between institutions and society, articulating and representing the people’s interests. Currently, Europarties are largely unknown to the population and are unable to conduct grassroots political activities. Targeted transformations should be implemented to supranationalize European political parties, enhancing the legitimacy of EU institutions and the ability of the Union to represent the interests of its citizens. The mission of the book is to present the challenges (and possible solutions) to supranationalizing EU party politics. To pursue this objective, it introduces the actors interacting within EU party politics, conducting a multidimensional and multilevel analysis of the interdependent relationships between European parties, European groups, European political foundations and national parties.