Institutional mechanisms for administering international climate finance constitute key components of an effect global climate regime, and the Green Climate Fund represents what promises to become the most important such mechanism. As the Fund begins to serve its function of transferring economic resources from developed to developing countries to support mitigation and adaptation activities, it faces several obstacles. Since contributions to the Fund by states or private parties are voluntary, they are not necessarily based on the UN Framework Convention on Climate Change’s “common but differentiated responsibilities” principle. Its governing instrument also departs from UNFCCC principles. In addition, the Fund faces a significant ambition gap in pledges to fund its operations. By instantiating several informal means of applying climate justice norms to assessments of national contributions to climate finance, some of this resistance might be overcome, increasing support for the Fund and, with this, increasing prospects for reaching consensus on a new climate treaty architecture at COP 21.