This chapter describes how knowledge about 'the city' as a social problem is generated in order to promote and legitimize social reforms. Studies on 'the city' and the living conditions of slum dwellers are spearheads of social science research and social work as an academic discipline. By focusing on the settlement house movement and the social survey movement, the chapter shows that 'the city' is an important boundary object that functions as a translation device through which social actors from these two social movements and from different countries were interlinked. The Hull House Maps and Papers and the work in the settlement were thus more closely integrated, institutionally and in other respects, than Charles Booth's study and the work of Toynbee Hall. The settlement house movement in Canada developed in parallel, and owed much to the energetic involvement of the Presbyterian Church.