Since 1987 the Mexican Migration Project has collected and disseminated representative survey data on documented and undocumented migration to the United States. The MMP currently includes surveys of 161 communities, which together contain data on 27,113 households and 169,945 individuals, 26,446 of whom have U.S. migratory experience. These data are here used to trace the evolution of the Mexico-U.S. migration system from the late 19 th to the early 21 st century, revealing how shifts in U.S. immigration and border policies have been critical to the formation of different eras of migration characterized by distinctive patterns of migration, settlement, and return in different legal statuses. The present era is characterized by the repression of the large population of undocumented migrants and their U.S. citizen children by an ongoing regime of mass detention and deportation and the simultaneous recruitment of Mexican workers for exploitation on short term temporary visas. The future of Mexican migration to the United States will be revealed by subsequent waves of data collection by the Mexican Migration Project.