Much of the literature on segregation is underlain by an implicit model which argues that groups start highly segregated in inner city locations and disperse over time. Parallel and related to this spatial pattern is the social process of assimilation. Groups start highly segregated and unassimilated and become dispersed and assimilated over time. The paper argues that there is a critical distinction between the black American ghetto and other forms of segregation. The ghetto is not part of a continuum of spatial distributions which begins in the inner city and ends in the suburbs three generations later; it is an end in itself. The black ghetto is different in kind from other forms of segregation. Nearly all of its members are black and nearly all the black population in American cities is in such locations. African American segregation has been almost continuously high during the twentieth century and has not diminished with socio-economic improvement. Ethnic enclaves of the Irish, Poles or other ethnicities in the USA never achieved such homogeneous concentrations. Thus representing European concentrations as having evolved from a past distribution, which was akin to the present black ghetto, falsifies the European past and mistakes the current dilute levels of European concentration as representing the black future. On the other hand, the equation of spatial segregation with levels of social assimilation, is largely supported. The process of assimilation, like the sequence of spatial segregation, is neither inevitable nor unidirectional.