This book is an exploration of the cultural meanings and legal consequences ascribed to the concept of individual, voluntary membership by the first generations of American citizens, between 1783 and 17840. It attempts to explain post-Revolutionary Americans’ propensity to form and join voluntary associations by looking at how they described and defended their ideas about what voluntary membership should look like. Within their own groups, joiners and organizers of American private associations found in law and in an emphasis on procedural fairness a way to cohere. And yet their legalistic framing of their own efforts to act collectively had another consequence: as more joiners in early national associations came to conceive of their participation as one of well-defined rights and obligations, legal institutions (chiefly, courts of law) occupied an increasingly important position in the monitoring of those internal relationships. Examining the contests over the meanings and consequences of voluntary membership reveals that, in the young United States, law provided the substructure for American civil society. Post-Revolutionary Americans, consciously and deliberately, sought to balance their need for effective, concerted action with their concerns for individual autonomy and personal rights. The answers that they settled upon then helped to shape their attitudes toward public and private law, toward constitutionalism, and toward individualism and cooperation in ways that transformed American society.