The Deep Decarbonization Pathways Project is a collaborative effort to understand how countries can transition to a low-carbon economy by mid-century and how the world can meet the 2 degree Celsius global warming limit. The project gathers the 15 largest emitters of greenhouse gases emissions, among them the US, China, Canada, and Brazil who represent more than 70% of emissions and required each country to write a DDP to 2050. There is a convincing case for action at the national level for two reasons, one being that deep decarbonization strategies need to be based on the most precise available estimates of mitigation potential within countries, and the other being that if they are to become the basis for public and policy discussion, they must be developed within countries by local experts, not imposed by external consultants who have less of a stake in the issues of climate change negotiations. There are different interpretations of the principle of common but differentiated responsibilities, which is central to the UN Convention on Climate Change: should we take into account historical emissions, exported carbon intensive products, developing countries’ differing mitigation potentials and costs, etc.? The issue of who will cover the investment cost of deep decarbonization is very concerning, but it is also critical to explore how each and every country will make that transition to a low-carbon economy. This video is part of the module Deep Decarbonization Pathways: Country Case Studies.