While sociology and urban planning might seem respectively to represent the theory and the practice of knowledge about cities, their relation has usually been distant. British sociology and urban planning were closely related before 1914, but largely because sociology was not a bounded specialty: community investigation methods were common throughout the British reform world, finding particular and successful application via city planning’s focus on housing and industrial location. In the United States, by contrast, sociology early became a clearly-defined academic discipline, and sociological empirical methods, although widely shared, supported only generalized reform demands, because local planning of housing and industry was politically impossible outside industrial communities. Most prewar city planning aimed at middle-class and aesthetic values rather than socially ameliorative community design. Between the wars, British academic sociology continued to develop slowly, and community sociological investigation fell largely to the rapidly developing profession of city planning, whose success and power culminated in the masterful plans for postwar London. In the United States, by contrast, sociology rapidly evolved towards national survey analysis, distancing itself even further from practical application in city planning. In general, then, the theory and practice of knowledge about cities remained separate in the first half of the twentieth century in Britain and the United States.