The removal of particulate radioactive material from exhaust air or gases is an essential feature of virtually all nuclear facilities. Recent IAEA publications have covered the broad designs of off-gas and air cleaning systems for a range of nuclear power plants and other facilities. This report is a complementary guidebook that examines in detail the latest developments in the design, operation, maintenance and testing of fibrous air filters. Contents: 1. Introduction; 2. Fundamentals of filtration; 3. Cha-racteristics of filtration systems; 4. Use of aerosol filters in nuclear facilities; 5. Ventilation and filter systems; 6. Handling, inspection and installation of new filter inserts; 7. Filter testing; 8. Handling, storage and disposal of contaminated filter inserts; 9. Trends and developments.