As the impacts of climate change escalate, efforts to develop new technologies and new approaches to reducing emissions are promoted. One proposal is to sequester carbon in soils using biochar. Biochar is essentially fine grained charcoal. Advocates claim that adding biochar to soils will store carbon safely away from the atmosphere for hundreds or even thousands of years, while boosting soil fertility and providing other benefits. What is the basis of these claims? Is biochar really a viable approach? This report is a substantially expanded update of our 2009 “Biochar for Climate Mitigation: Fact or Fiction”. It takes a critical look at the claims around biochar, reviews the science underlying the claims, provides an overview of what biochar advocates are pushing for in terms of policies and supports, and presents an outline of the companies involved. It is an interim report, with the final version due to be published during the UN climate conference in Durban.