Trickle vents in window frames and airbricks in walls have been used to ventilate dwellings for many decades. However, the concept of background ventilation as part of an overall ventilation strategy did not appear in Approved Document F of the Building Regulations until 1990. Initially, only simple manually adjustable background vents were used in the UK to meet these regulations, but more innovative vents incorporating automatic flow control or other novel features are now appearing on the market. This paper discusses the philosophy behind background ventilation in Building Regulations and the types and merits of background vents currently available. Vents controlled by humidity, temperature or pressure difference are briefly discussed. Acoustic vents with improved sound attentuation properties may be necessary to provide natural ventilation in noisy areas near roads or factories. A forthcoming European Standard will cover the performance testing of background ventilators for their aerodynamic characteristics, sound insulation and watertightness. 6 pages.