It is in the world’s poorest regions that smoke is a major threat, including China, India and sub-Saharan Africa. On current trends,200 million more people will rely on these polluting fuels by 2030. Women and children are exposed for up to seven hours a day to pollution concentrations 100 times and more above accepted safety levels. There is ample medical evidence that smoke from burning biomass fuels leads to killer diseases, such as penumonia, chronic bronchitis and lung cancer. Smoke is a chronic problem in rural areas of developing countries. Most people who depend on biomass fuels live in the countryside where wood and agricultural residues are readily available. However, there is a growing problem in cities as well, as many people moving from rural areas to urban settlements continue to use traditional fuels. There is a complex relationship between indoor and outdoor pollution in urban areas. In cities, indoor air pollution can be due partly to external pollution sources such as vehicle emissions. In turn, the outdoor air pollution in parts of cities can consist largely of the emissions from fires in people’s homes.