The idea of taking responsibility for the planet is inbuilt in the very notion of sustainability. This chapter addresses the basic meanings of the notion (imputability and answerability) and its twofold time orientation (backwards and forwards), and reflects on how some features of modern society, namely functional differentiation and the relevance of future and its predictability, affect it. The problem of collective responsibility is also dealt with. Attention subsequently turns to how the issue of responsibility has evolved in the context of recent societal transformations. Changing views about reality, its knowability, its temporal deployment, and how these impinge on purposeful action entail significant shifts in the configuration of responsibility, with an expanded room for irresponsibility. However, traditional forms of responsibility are not ruled out. Moreover, new social norms may be conducive to more sustainable ways of living on the planet.