It is often said nowadays that there is no special urban sociology. What goes on in the city, it is claimed, is merely an expression of general processes at work in a national industrial society. An adequate theory of this society would therefore comprehend within itself the sociology of the city. I believe there is some truth in this view, but I also believe that there are particular processes at work in the concrete urban situation. I propose to illustrate this by OUt1ill~ ing a theoretical model which explains something at least of the community structure of what Burgess called 'the zone of transition'. This model includes three elements: (1) a general theory of housing classes in the city, (2) a theory of ethnic group relations and rural-urban culture change and (3) a theory of conflict and conflict resolution as between associations in the urban zone of transition.