The recent influx to the United States of a new large wave of immigrants from Hispanic America and Asia has reinvigorated immigration and ethnic studies, including those devoted to the analysis of the origins and process of international migrations. The accumulation of research in this field in the last fifteen years has brought about a shift in the theoretical paradigm designed to interpret these movements. The classical approach explains the mass flow into North America of immigrants (from Southern and Eastern Europe, in the period 1880 to 1914), as an international migration interpreted in terms of push and pull forces. Demographic and economic conditions prompted individuals to move from places with a surplus of population, little capital, and underemployment, to areas where labor was scarce and wages were higher (Jerome, 1926; Thomas, 1973; Piore, 1979; Gould, 1979). This interpretation views individual decisions and actions as the outcome of a rational economic calculation of the costs and benefits of migration. Recent studies of international population movements have reconceptualized this problem, recasting the unit(s) of analysis from separate nation-states, linked by one-way transfer of migrants between two unequally developed economies, to a comprehensive economic system composed of a dominant core and a dependent periphery— a world system that forms a complex network of supranational exchanges of technology, capital, and labor (Castells, 1975; Cardoso and Faletto, 1979; Kritz, 1983; Sassen-Koob, 1980; Portes, 1978; Portes and Walton, 1981; Wood, 1982). In this conceptualization, the development of the core and the underdevelopment of the peripheral societies are seen not as two distinct phenomena, but as two aspects of the same process—the expanding capitalist world system, explained in terms of each other. Generated by the economic imbalances and social dislocations resulting from the incorporation of the peripheries into the orbit of the core, international labor migrations between the developing and industrialized regions are viewed as part of a global circulation of resources within a single system of world economy. This interpretation shifts the central emphasis from the individual (and his/her decisions) to the broad structural determinants of human migrations within a global economic system.