A range of developing countries and international advocacy organizations have argued that wealthy countries, as a result of their greater historical contribution to human-induced climate change, owe a ?climate debt? to poor countries. Critics of this argument have claimed that it is incoherent or morally objectionable. In this essay we clarify the concept of climate debt and assess its value for conceptualizing responsibilities associated with global climate change and for guiding international climate negotiations. We conclude that the idea of a climate debt can be coherently formulated, and that while some understandings of the idea of climate debt could lead to morally objectionable conclusions, other accounts would not. However, we argue that climate debt nevertheless provides an unhelpful frame for advancing global justice through international climate negotiations ? the only existing means of resolving political conflict over the collective action problems posed by human-induced climate change ? due to its retrospective and potentially adversarial emphasis, and to problems of measurement.