In 1997, the introduction of the new National Ambient Air Quality Standard for PM2.5 in the USA resulted in controversy, not only with respect to the stringent Limit selected, but also due to the many problems associated with ensuring compliance with a standard for a pollutant which is so poorly understood. Europe has no standards for PM2.5 at present, but new standards have been proposed for 2005. This paper addresses the research in progress which will determine whether other countries will follow the USA's lead in setting such standards. It discusses sampling and analysis techniques, followed by a summary of PM10 and PM2.5, as well as their control in coal-find power plants, concentrations in the atmosphere and health effects. (C) 2000 Elsevier Science B.V. All rights reserved.