This chapter examines the role of political parties in the processes of democratization, that is, during transition, installation, and consolidation, and the possible phases of democratic crisis. It first considers the definition of a political party within the processes of democratization before discussing how parties can be indispensable for the actual working of democracy. It then explores the actual role of political parties during transitions to democracy and during democratic consolidation, and in different types of crises. It also describes basic patterns of transition to democracy as well as key elements of democratic consolidation, including electoral stabilization and emergence of recurring patterns of party competition. The chapter shows that parties are dominant in the process of transition, even if not always hegemonic.