Party membership has long been an important channel for political participation in many countries. Strong membership organizations have helped parties win elections and stay connected with voters between elections, and membership opportunities have helped to mobilize some citizens who might otherwise have stayed out of politics. Yet in the last quarter-century, long-established political parties in parliamentary democracies have, with a few notable exceptions, experienced sharp enrollment declines, while newer parties have developed modest memberships at best. This has led many observers to question the continued viability of membership-based political parties. However, that is not the whole story. While some signs point to the obsolescence of party membership, there are other indications that parties are trying to reinvent the form, whether as a passport to individual political empowerment or as a pathway to digital citizenship. Most strikingly, many parties are experimenting with new procedures that give members a direct say in important party decisions. In this sense, the paradoxical story of party membership in the early 21st century is one of numerical decline accompanied by a possible increase in political relevance.