Parties to the Paris Agreement can engage in voluntary cooperation and use internationally transferred mitigation outcomes towards their national climate pledges. Doing so promises to lower the cost of achieving agreed climate objectives, which allows countries to increase their mitigation efforts with given resources. Lower costs do not automatically translate into greater climate ambition, however: Transfers that involve questionable mitigation outcomes can effectively increase overall emissions, affirming the need for a sound regulatory framework. As Parties negotiate guidance on the implementation of cooperative approaches under the Paris Agreement, they must consider governance options to secure environmental integrity and address the question of overall climate ambition. But country views are far apart on central questions. Of all the issues under negotiation to operationalize the Paris Agreement, cooperative approaches are the only agenda item still under debate. Drawing on an analytical framework that incorporates economic theory, deliberative jurisprudence, practical case studies, and treaty interpretation, this Article maps central positions of actors in the negotiations and evaluates relevant options included in recent textual proposals. It concludes with a set of recommendations on how operational guidance can balance necessary safeguards for climate ambition with flexibility to contain transaction costs and allow for greater participation.