This chapter discusses the decline of political parties as a possible cause of the decline of legitimacy. Political parties constitute a link between the citizens and the political system, and therefore a loss of support could delegitimize the political system. However, the decline of political parties can only cause legitimacy decline if they are indeed in decline and if there is a causal relationship between citizens’ involvement in political parties and political support. The chapter argues that empirical evidence for party decline is limited, as parties may have undergone transformation rather than decline. Using ESS data from 2002 to 2010, the chapter finds only weak relations between political support and party membership and party closeness. However, being close to a particular party is more important than being a member of a political party, and is interpreted as a sign that the party system facilitates citizens in making meaningful political choices.