Twenty-one senior researchers were interviewed about their conception of sustainability and implementation in projects linked to the Alliance of Global Sustainability, a joint project of MIT (Boston), ETH (Zurich and Lausanne), UT (Tokyo), and Chalmers (Gothenburg). We identified five complementary views on sustainability: i) science is sustainable per se, ii) sustainability is an ethical relationship with the past and future, iii) sustainability is the maintenance of a system within functional limits, iv) eco-efficiency, and v) sustainability is a form of ongoing inquiry. In total, the concept of ethical relationship was the most dominant, whereas science per se and eco-efficiency were less used. Natural, engineering and social scientists referred differently to these concepts in their research projects. Most of the researchers regarded implementation as the process of interacting with stakeholder groups. The relationship between knowledge and action is considered central to views on implementation. Three different concepts and habits could be identified with respect to the relationship between knowledge and action: a) action, I act to change the world; b) interaction, I exchange information with my environment through my actions; and c) transaction or mutual learning, I change as a result of my effort to bring about change in the world.