Almost 3 billion people, in low- and middle-income countries mostly, still rely on solid fuels (wood, animal dung, charcoal, crop wastes and coal) burned in inefficient and highly polluting stoves for cooking and heating. In 2012 alone, no fewer than 4.3 million children and adults died prematurely from illnesses caused by such household air pollution, according to estimates by the World Health Organization. Together with widespread use of kerosene stoves, heaters and lamps, these practices also result in many serious injuries and deaths from scalds, burns and poisoning. These new indoor air quality guidelines for household fuel combustion aim to help public health policy-makers, as well as specialists working on energy, environmental and other issues understand best approaches to reducing household air pollution -- the greatest environmental health risk in the world today.