To say international migration is to say cross-border connections: the ties linking sending and receiving countries are a salient aspect of the migration experience, appearing during present as well as past eras of migration. This article reviews the sociology of these cross-state ties and spillovers, typically associated with the literature on transnationalism. The article discusses the intellectual history of the transnational perspective on migration, offers a critical evaluation and then presents a different approach, designed to identify the mechanisms generating and attenuating cross-border connections across a range of activities. Focusing on the experience in the Americas, the article then turns to the empirical literature, synthesizing the results of research on cross-border social ties, homeland politics, and homeland spillovers. The last section suggests new avenues for future research.