This article reviews theoretical perspectives on migration and development, starting with nineteenth-century political economy theories focused on “colonizing” migrations from England and other European powers and concluding with the emerging literature on immigrant transnationalism and its consequences for sending nations. The general concept of equilibrium has until currently dominated orthodox economic theories of both colonizing and labor migrations from peripheral regions to advanced nations. The counteroffensive, led by Gunnar Myrdal and theorists of the dependency school, centered on the notion of cumulative causation leading to increasing poverty and the depopulation of peripheral sending areas. Both perspectives registered numerous empirical anomalies, stemming from a common view of migration flows as occurring between separate politico-economic entities. An alternative conceptualization of such flows as internal to an overarching global system has improved our understanding of causes and consequences of labor migration and has framed the back-and-forth complexities of these movements captured in the novel notion of transnationalism.