This paper adopts a positivist approach to social geography, which is viewed as a study of the two-way relationship between spatial structure and social structure. This relationship is examined in cities in contemporary Britain and the United States. The concept of social structure is discussed in the first section. It is suggested, after Blau, that social structure may be delineated by parameters which demarcate the lines of differentiation among people, created in their social interaction. Area of residence may be considered such a parameter. Social structure comprises a complex configuration of these parameters. In general, coinciding parameters limit social mobility and lead to an atomised society. The processes by which social structure takes on spatial expression are discussed in the second section. The salience of various parameters of social structure in a spatial setting is assessed first. Behaviouralist, managerialist and structuralist approaches to residential differentiation are reviewed. It is argued that most insight will come from studies of the interaction between groups of households and the major institutions of the housing market in the context of characteristics of the housing supply. The impact of neighbourhood on social structure is examined in the third section. The role of propinquity in social interaction is discussed along with the role of neighbourhood as a status symbol. Individuals may change their position along structural parameters as a consequence of their residential location. Residential segregation is also a means, through its role in circumscribing contacts, by which the continuation of the stratification system is ensured in the next generation. In conclusion, it is noted that the isolation of racial minorities in the disadvantaged parts of the city poses a danger to social stability.