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"In this review, we examine theories, data, and research on the macroeconomic relationship between international migration and national development in all world regions. Earlier reviews have generally been pessimistic about the prospects for economic development as a result of international migration. Until recently, however, theories and data have not recognized the complex, multifaceted, and often indirect ways that international migration can influence the economic status of households, communities, and nations, and they have generally failed to appreciate how these relationships can change over time. When these complexities are incorporated into theoretical models, research designs, and data collection, a more nuanced and far more positive picture emerges. Given a supportive mix of macroeconomic policies and infrastructure, international migration may function as a dynamic force promoting economic growth and national development, so long as it does not bring about the selective emigration of scarce human capital needed for development at home."

Although social scientists usually do not speak in terms of laws, they believe they are at least able to make valid empirical generalizations. In studies of Mexican migration to the United States, for example, generalizations drawn from the research literature abound. Thus the problem is not that generalizations are lacking but that they are frequently inconsistent and contradictory. Often such inferences are simply invalid because they are based less on evidence than on the investigator's own preconceptions. As a result, the field of Mexican migration studies has been plagued by a fragmented debate that seems to go on and on without resolution.

Economists have long recognized the importance of migration between less developed and more developed countries, and they have devoted considerable attention to analyzing it within the framework of traditional economic theory (Thomas 1954; Kindleberger 1967; Tapinos 1974; Greenwood 1979; Chiswick 1980; Wachter 1980; Stark 1983). But international migration entails not only an economic exchange of work for wages, it is also fundamentally a social process. Repeated human contact inevitably produces ties between persons in sending and receiving societies. Social networks are created that connect individuals in disparate cultural settings, and these ties ultimately change the context within which economic processes are played out. Understanding how such ties develop and change over time is therefore crucial to understanding the phenomenon of international migration.