To promote cooperation in international climate negotiations, negotiators should focus on a common commitment. Such commitments have the advantage of facilitating reciprocal “I will if you will” agreements in a group. Reciprocity is the basis for cooperation in repeated public goods games, and a uniform price would provide a natural focal point for a common international commitment. Such a price is also essential for efficient abatement. Countries would retain flexibility in how to implement the price—with cap-and-trade, a carbon tax, or a hybrid approach.