Against the backdrop of sharply rising land and housing prices in attractive German cities, ownership of urban land has been the subject of public debates for some years now. Recently, more and more voices have been calling for a “re-appropriation of the urban” by reorganizing urban land as a commons. In this article, we examine the guiding idea of the “city as commons” associated with these demands from the perspective of economic ethics. First, we use Catholic property ethics to illustrate the social obligation of private property and concretize it using the example of ownership of urban land. From the perspectives of the economic classification of goods and commons research in the tradition of Elinor Ostrom, we then look at the idea of the “city as commons” and thereon provide an ethical reflection on city space as a nexus of cooperation. We explain why a city as a nexus of cooperation should be protected from overly strong particular interests and present a brief outline of land policy action.