ABSTRACT The approaches currently dominating sustainable urban planning are based on a paradigm which assumes that economic growth can be decoupled from economic degradation through smarter technological solutions and institutional reform within existing social structures. However, decoupling can only be partial. Environmental sustainability, therefore, requires that, sooner or later, growth in consumption and production must cease. Policies for combining environmental and social sustainability would be sharply at odds with key mechanisms inherent in the capitalist economy. Urban sustainability thus requires profound (...) changes. On the ontological plane, planning theory must move away from anti-realist constructivism and hermeneuticism, towards realism. On the empirical plane, it is necessary to move away from disciplinary tunnel vision towards a critical realist version of interdisciplinarity, within key research fields such as housing research and transportation research. On the political plane, urban sustainability must move from growth to degrowth, from inequality to equality, and from capitalism to eco-socialism. (shrink)