This report argues that International Cooperative Initiatives (ICIs) could hold significant promise for closing the global emissions gap between a pathway to a 2°C warming limit and current national emission reduction pledges. It examines a selection of these ICIs to explore their potential for delivering additional greenhouse gas mitigation and for raising ambition at national and international levels. It concludes that there are a range of ICIs already making an important contribution. It argues that many have potential to scale-up their activities and could offer promising new channels for public climate finance.