Some three billion people use biomass fuel – typically from wood, crop residues, or animal dung – to cook indoors in open fires and leaky stoves. Inefficient and highly polluting, the emissions from home cooking fires are a major contributor to the 4.3 million deaths that occur annually from household air pollution. In Rwanda, a clean-burning biomass stove offers an alternative that saves lives, while reducing laborious fuel-gathering chores. By using fuel pellets as a source of renewable energy, the stove also curbs deforestation and greenhouse gas emissions. A look at the technology, the business model, and the potential boon to human health.