The residential segregation of immigrants in American cities, long a classical ecological problem, is reexamined for specific immigrant groups in each of 10 cities in an effort to ascertain the impact of segregation on other aspects of ethnic assimilation. Ability to speak English, citizenship, intermarriage, and occupational composition of 10 immigrant groups in each city are viewed as a function of their residential patterns and other ecological factors. The dynamic significance of spatial distribution for other dimensions of social behavior is stressed. T HE IMPORTANCE human ecologists attribute to the spatial distributions of human populations and social institutions is not only widely known but, if anything, misunderstood by many of their fellow social scientists. The ecologist's interest in space is often taken as evidence either of a preoccupation with the subsocial or of an esthetic satisfaction derived from locating social events in terms of gradients, natural areas, multicolored maps, and the like. That this monolithic pursuit is to be found in the works of human ecologists-both present and past-ignores the far less constricted rationale which may be offered for this concern. For example, during the heyday of European immigration to the United States, the propensity of immigrants to first locate in ghettoes and their later movements out of these areas of first settlement were frequently utilized as a measure or index of an ethnic group's assimilation. Studies of such diverse urban centers as Chicago,' Durban,2 Montreal,3 Paris,4 and the major cities of Australia5 attest to the wide-spread existence of residential segregation and its usefulness as an indicator of ethnic assimilation. Indeed, during the twenties and thirties, ethnic residential patterns were a major research interest of sociologists and others. However, another dimension to the residential segregation of ethnic and racial groups is frequently overlooked. That is, not only can the residential patterns of ethnic groups be viewed as a significant element in the study of their assimilation and as an indicator of other elements of assimilation but, further, residential segregation has an effect on other aspects of ethnic assimilation. Hawley has hypothesized that physical isolation is a necessary condition for the maintenance of subordinate ethnic group status and, further, that Redistribution of a minority group in the same territorial pattern as that of the majority group results in a dissipation of subordinate status and an assimilation of the subjugated group into the social structure.6 Hawley's reasoning is based on the dual effect of residential segregation, that is, both as a factor accenting the differences between groups by heightening their visibility and, secondly, as a factor enabling the population to keep its peculiar traits and group structure. Evidence exists to support both of Hawley's contentions. For example, after finding that the greater the number of Negroes arrested in a district in Philadelphia, the greater the overestimation by policemen of the Negro * This study was supported by a grant from the Ford Foundation to the Research and Training Center, University of Chicago. This is paper number 8 in the series Comparative Urban Research. I Otis Dudley Duncan and Stanley Lieberson, Ethnic Segregation and Assimilation, American Journal of Sociology, 64 (January 1959), pp. 364-374. 2 Leo Kuper, Hilstan Watts, and Ronald Davies, Durban: A Study in Racial Ecology (London: Jonathan Cape, 1958). 3 Eva R. Younge, Population Movements and the Assimilation of Alien Groups in Canada, Canadian Journal of Economics and Political Science, 10 (August 1944), pp. 372-380. Robert Gessain and Madeleine Dore, Facteurs Compares d'assimilation chez des Russes et des Armeniens, Population, 1 (January-March, 1946),