Scholars have long noted how migration streams, once initiated, obtain a self-feeding character. Studies have attributed this phenomenon – the cumulative causation of migration – to expanding social networks that connect migrants in destination to individuals in origin. Studies however, often disagree on how social networks influence migration decisions. While many establish a positive association between individuals’ ties to prior migrants and their migration propensities, only few acknowledge that multiple social mechanisms might account for these interdependencies. To address this issue, we adopt a typology developed by DiMaggio and Garip (2012) and consider three mechanisms by which social ties may influence individuals’ migration choices. We study the prevalence of these mechanisms in the Mexico-US migration context using a mixed methods approach. First, analyzing data from more than 90,000 individuals surveyed by the Mexican Migration Project (MMP) we establish the presence of network effects in migration and test how prior migrants in the family or community increase individuals’ migration propensities, and whether prior migrants reduce the effect of economic or political indicators on migration propensities. Second, we analyze qualitative data from 120 in-depth interviews to determine the different mechanisms that lead to interdependencies in individuals’ migration choices. We thus provide a deeper understanding of migration as a social process, which we contend is crucial for anticipating future flows and policy responses.