The German Environmental Agency (UBA) commissioned a consortium of NewClimate Institute, Öko-Institut and Fraunhofer ISI to analyse the impact of international, regional and national initiatives outside the United Nations Framework Convention on Climate Change (UNFCCC) on greenhouse gas emissions. While it seems clear that these initiatives can motivate a large number of stakeholders to engage in the area of climate change mitigation, the expected emission reductions from the initiatives are unclear, as well as their overlap with national pledges and measures. A further question is how the initiatives can or should be linked to the UNFCCC process. This project aimed at increasing clarity on the role of international initiatives by investigating – quantitatively and qualitatively – the potential impact of the initiatives on GHG emissions, the elements that make an initiative successful and the options to integrate initiatives into the UNFCCC process and accounting procedures.