Who bears responsibility for climate change? Confronting this question is central to establishing equitable policies to reduce greenhouse gas emissions and limit the adverse impacts of now unavoidable climate disruption. International climate policy frameworks focus on the “common but differentiated responsibilities” of nations. But climate responsibilities also extend to non-state actors, including individuals, utilities and fossil-fuel companies at the base of the carbon supply chain whose responsibilities are increasingly the focus of attention by civil society, policymakers and the courts. This course examines the nature of climate responsibility from ethical, historical, scientific and policy perspectives and the efficacy of approaches to accelerate responsible climate action by both state and non-state actors.