Over the past two decades, ‘sustainability’ has become an idea central to social practices on the part of governments, policy-makers, organisations in the public, community and private sectors, and citizens. We begin with a discussion of sustainability. We then ask why it has become such an important contemporary idea. We discuss one recent explanation for the preoccupation with ‘sustainability’ offered by Ulrich Beck in terms of his theory of ‘risk society’. We then turn to the role played by new social movements like the environmental movement. Finally, we explore the paradox that the successes of the environmental movement have occurred at the very time that a major ‘sea change’ has been taking place in the political and policy-making cultures of most Western societies, understood as a shift away from a mixed economy (informed by a Keynesian tradition of social liberalism) involving intensive state involvement in economic management, and towards an ‘economic liberal’ policy model which emphasises market-based activities.