This chapter looks at the nature and evolution of political parties in a number of European democracies. It analyses the important functions of political parties. It charts how they have developed over time. Starting with the social cleavage approach, the chapter addresses the origins of European party families and party systems. It then turns to the transformation of European party families and systems. It considers this both nationally and within the European Union (EU). It provides evidence of the ‘unfreezing’ of European party systems and thinks about whether a dealignment of traditional cleavage patterns can currently be witnessed. It asks: is there also a realignment along a new ‘cultural’ dimension of politics? Finally, the chapter addresses the evolution of party types from cadre over catch-all to modern entrepreneurial challenger parties.