Air pollutants may be present in the atmosphere as gases or particles. Most air pollutants are directly emitted into the atmosphere, but some are formed there by chemical reactions. Air pollutants are transported across regions and countries and may cross national boundaries. In this chapter, we discuss air pollutants, their health impacts and their principal sources. We also highlight the main greenhouse gases and pollutants: carbon dioxide, methane and ozone. While there is much focus on the reduction of the emissions of those particles which can penetrate the lungs, reducing aerosol particles also affects global warming. Coal and oil combustion are major causes of air pollution problems, followed by road transport using gasoline and diesel fuels. Massive reductions in carbon dioxide and all pollutants will be achieved over the next two decades by transforming power stations and road transport. It is, however, important to consider all sources of pollution, both anthropogenic and natural biogenic, in order to improve air quality.