An intensive standardisation process is currently in progress within the air cleaning field, During the past few years new test methods and classification systems have been developed for all types of filters, from coarse filters to absolute and ULPA filters. CEN (Comite Europeen de Normalisation) is working to establish common standards throughout Europe, while Eurovent is leading the development of new and modern test methods that can meet today＇s requirements for ventilating air filter installations in indoor environments and other areas, In the United States, ASHRAE is launching a new test method to determine the fractional efficiency of filters using a new concept for test methods and classification. The Institute of Environmental Sciences has introduced a number of test methods, ranging from flat sheet tests of filter materials to tests of filter installations, that have to meet very stringent performance requirements.