To close the gap between existing country pledges and the necessary ambition level to limit anthropogenic climate change to not more than 2°C average global temperature increase above pre-industrial levels, decision makers from both the public and private domain have started to explore a number of complementary approaches to the top-down targets-and-timetables approach of international climate change policy. Referred to as International Cooperative Initiatives (ICI), these governance arrangements are now also officially acknowledged under the United Nations Framework Convention on Climate Change (UNFCCC) Durban Platform for Enhanced Action. While proponents see ICIs as important bridging devices towards more ambitious climate policy, in particular up to 2020, critical observers note that the voluntary nature of ICIs makes it difficult to assess their contribution to climate change mitigation. This article scrutinizes the potential of ICIs to meaningfully contribute to closing the emissions gap along the criteria of effectiveness, legitimacy and institutional fit. As means of illustration, the analytical framework is applied to a random sample of nine ICIs (out of a total of 45 listed on the UNFCCC Secretariat’s website). We find that while potential technical effectiveness is high, legitimacy and institutional fit should be improved with a view towards integrating ICIs into the emerging post-2015 climate governance architecture.