Recent scholarship on Mexican Americans in the United States, relying largely on qualitative evidence, sees racism and exploitation as the major explanatory factors in their history. Using representative samples of persons of Mexican origin, we argue that immigration is fundamental to their historical experience. A small, beleaguered community in 1850, the Mexican-origin population grew during the late nineteenth century due to greater security under US jurisdiction. However, immigration between 1900 and 1930 created a Southwest broadly identified with persons of Mexican origin. Economic development in Mexico, restriction of European immigration to the United States, and extreme cross-border wage differentials prompted extensive emigration. Despite low human capital, circular migration, and discrimination, immigrant Mexicans earned substantially higher wages than workers in Mexico or native-born Hispanics in the United States. They followed typical immigrant paths toward urban areas with high wages. Prior to 1930, their marked tendency to repatriate was not “constructed” or compelled by the state or employers, but fit a conventional immigrant strategy. During the Depression, many persons of Mexican origin migrated to Mexico; some were deported or coerced, but others followed this well-established repatriation strategy. The remaining Mexican-origin population, increasingly native born, enjoyed extraordinary socioeconomic gains in the 1940s; upward mobility, their family forms, and rising political activity resembled those of previous immigrant-origin communities. In the same decade, however, the Bracero Program prompted mass illegal immigration and mass deportation, a pattern replicated throughout the late twentieth century. These conditions repeatedly replenished ethnicity and reignited nativism, presenting a challenge not faced by any other immigrant group in US history.