The problematic of sustainable cities depends on global environmental problems which recently have become acute. The first part of the article retraces the origin of this problematic, in order to determine its defining characteristics. A hypothesis is formulated, that this new reference frame for urban public policy carries with it a turning-point for urbanism in general, raising various tensions and contradictions. In the second part, concrete realisations of this turning-point are addressed, via the modes of action, or inaction, of the European cities which have been striving for sustainability over the last 15 years. An assessment of urban policies which have been employed is undertaken, underlining their benefits and their limits.