The goals of sustainable development are rarely simply and clearly defined, but more often—although to varying degrees—ambivalent, difficult to agree and hard to specify. This paper reflects on the inherent ambivalence of sustainability as a normative objective of steering and governance. It draws, in particular, on Bauman's account of the complex relationship between ambivalence, modernity and postmodernity, using these ideas to consider the strategic work involved in drawing boundaries around what is sustainable/unsustainable. The implications of the analysis are explored for conventional and reflexive approaches to the governance and management of socio-technical transitions. Strategies of reflexive governance promise to engage more openly and directly with the challenges of handling rather than eliminating ambivalent and changing goals. While these approaches bring some dimensions of ambivalence out into the open, they do so by framing debate in ways that background others, thereby obscuring the politics involved. The article concludes by turning the problem around and arguing that rather than being something managed through methods of governance, ambivalence is itself an outcome and a consequence of such techniques.