The Deep Decarbonization Pathways (DDP) project was launched in October 2013 as a joint collaboration between IDDRI and SDSN, under the leadership of Laurence Tubiana and Jeffrey Sachs. Its primary objective was to support a positive outcome at COP21, by demonstrating that country-driven deep decarbonization pathways to 2050 can be a relevant instrument to guide national ambition and actions. To do so, a group of domestic research teams from 16 countries – all large emitting G20 countries, both developed and emerging – was gathered to elaborate country-driven pathways consistent with the global goal of stabilizing global warming to 2°C. Until the end of 2015, this group defined the methodological foundations of the DDP in response to the intrinsic challenges posed by the approach itself (ie addressing a global problem as a composite of national analyses). And it produced a landmark report which proposes detailed analyses of energy transition pathways for each of the 16 countries, as well as a cross-country analysis of challenges, opportunities and solutions for global decarbonization consistent with a temperature limit of 2°C anchored in the realities of countries. With the international and in-country dissemination of these findings, the DDP contributed to the Paris Agreement.