Jewish migrants to the United States reveled in their ability to move, but also struggled to adapt to the distinctive social and economic relations of the United States, which was a “world of strangers.” This chapter shows how Jews created a wide range of social ties and institutions—not just congregations—in search of stability, trust, and identity. They entered into friendships and voluntary societies with non-Jews, but also sought out coreligionists through informal ties, newspapers, kosher boardinghouses, fraternalism, and worship services. Gradually, they moved to create Jewish organizations that were public and recognized by the state, including mutual aid societies, literary societies, fraternal lodges, charities, and congregations. Voluntarism did not perfectly map onto Jewish communalism, however, even more so because mobile Jews were rarely consistent, stable, or religiously uniform. This was especially problematic for congregations, which struggled to determine the boundaries and meaning of “membership” as well as the nature of congregational identity, liturgy, and worship.