The 1990s has witnessed significant increases in immigration in almost all Western countries. This immigrant inflow has in many instances become the largest component of national population growth and a major factor in social and cultural change. The destinations of these immigrants are also highly concentrated geographically, adding to the uneven patterns of urban growth and change.The impacts of the concentration of new immigrants in a few large metropolitan areas have yet to be evaluated, but they are likely to be considerable. These effects can also be either mitigated or further augmented by the internal migration of the nativeborn and earlier immigrants to and from these major immigrant-gateway centers. The volume of net internal-migration flows not only impinges on the uneven geographical distribution of population growth, but selective out-migration and in-migration may also influence spatial differences in the sociodemographic and ethnic composition of the country's population.Recently, selective migration seems to be a common pattern in major immigrantgateway cities in the United States and Australia, and in some European countries: the domestic-born, the less-well-educated in particular, are moving away and leaving behind a markedly more heterogeneous social environment in metropolitan areas that stands in contrast to the rest of the nation (Champion, 1994;Frey, 2002a;Ley, 2003; The Economist 2003). Indeed, Frey (2002a) suggests that the differences in immigration and internal-migration flows in the United States are transforming what was a once`single melting pot' nation into three distinct Americas: a suburb-like`New Sunbelt' region, a socially diverse and economically vibrant`Melting Pot' region, and an aging, whiter, and slow-growing`Heartland' region. Similar concerns about increasing geographic divisions in levels of social diversity have also been raised in other major immigrant-receiving countries.