It will be argued in this paper that the problematic of social cohesion is also one of socio-ecological cohesion whereby the urbanisation of nature and its socio-environmentally enabling and disabling conditions are key processes. By viewing the contradictions of the urbanisation process as intrinsically socio-ecological ones, the terrain of social cohesion is shifted both epistemologically and politically. The paper critically examines three contemporary schools of thought that consider in different ways the relationship between cities, social cohesion and the environment. It begins with a critical examination of the notion of urban sustainability. The paper will then move on to consider two approaches that emphasise issues of (in)equality and (in)justice in the urban environment, those of environmental justice and urban political ecology. The final part of the paper pinpoints four areas of research that urban researchers must examine if we are to understand more fully—and act more politically on—the nexus between cities, social cohesion and the environment.