This book originated with a concern for a crucial issue in planning; namely, what is the possibility of creating social policies to modify existing patterns of segregation in order to achieve social justice (however defined) in such institutions as housing or schools. Consequently, although this is an academic, ecological analysis of residential segregation as reflected in demographic statistics, the larger social issue helped shape the specific questions raised in the text, e.g.: Is ethnic separatism--such as Italian Catholic from Irish Catholic--still a viable force? What is its relevance, if any, to the segregation of blacks and Puerto Ricans? (Ethnic groups will usually mean European immigrants and their children, although on occasion Puerto Ricans will be treated as another white ethnicity.) How do social class difference (family income or educational attainment statistics) affect racial and ethnic segregation? If one wishes to create planned change, what are the existing processes that create segregation patterns now and that have to be manipulated? The data and methods used here are limited to ethnic (foreign-stock and Puerto Rican) and racial (black) segregation index numbers, calculated from the census-tract statistics of the 1960 New York-Northeastern New Jersey Consolidated Statistical Area. So that a conclusion may be reached with this limited amount of original evidence, several parts of the author's and others' findings are synthesized. The New York Standard Metropolitan Statistical Area of 1960 is related to the recent past of other cities. (Author/JM)