How should we respond to the increasingly dense bundle of economic, cultural and ecological interconnections that span the globe and stretch into the future? What kinds of ethical and public engagements are demanded of researchers who work on global environmental, economic and social issues? The term interdependence may provide a powerful framework for advancing thinking and debate both within academia and among wider publics in relation to these questions. Members of the Open University's Geography Department have been working with partners to build the Interdependence Day project. The project combines research, cultural work, communications and public participation in an attempt to make sense of our responsibilities to people distant in space and time, and to the nonhuman natural world. This article reviews nearly a century of deployments of the term interdependence in political and academic writing, introduces the distinctive work that might be done with the term in the critical social sciences, and outlines the Interdependence Day project.