INTRODUCTIONThe development of particulate filters has had several stimuli - the protection of workers from harmful dust, the call for medical respirators, the protection of fire-fighters from smoke, the protection in times of war and crime, the sampling of dust and aerosol particles, etc. For this reason, it is no wonder, that the history of dust and aerosol filtration is over two thousand years old.EARLY DAYSThe earliest records of air filters date from Roman times. Leonardo da Vinci mentions wet clothes as a protection from fumes used in warfare. Agricola describes primitive respirators for miners. Next pioneers in dust protection by using filters were Paracelsus, Ramazzini and Pasteur.FILTRATION SCIENCEFirst more sophisticated aerosol filter was invented in England by E. M. Shaw and John Tyndall. The scientific development of aerosol filtration and filters started in the 30s of this century in Germany (Albrecht, Kaufmann) and in Denmark (Hansen). Fast development in filtration theories as well as in filter production can be observed during and after the World War II (Langmuir, Davies, Friedlander, Whitby, Fuchs, etc.).First applications of filters for aerosol sampling date already from the Middle Ages. Nevertheless, important developments started also only after the 1930s (Reznik, Goetz, Spurny, etc.)In 1930, N. L. Hansen working in Copenhagen tried the powdering of a wool filter pad with colophony resin and he found a very great increase in filtering efficiency. It was in fact the invention of the first electret filter, as the resin was an electrically insulating substance.THE STATE OF ARTSAt the end of the 20th century, the development of aerosol filtration science (Spurny, 1997) is characterized by very successful improvement of the single filtration element theory (Fig. 1) and the beginning of new theoretical concepts and approaches using the concept of the integrated cell models .In the later approach, the filtration process is described as particle separation in the whole inner structure of the filter by counting the particle transport and particle capture equations.Nevertheless, the classical single filter element filtration theory is and will still remain a very important and useful tool for the prediction of particle separations and pressure drops in real filters.