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Encouraging the use of natural ventilation is an important tendency in the green building movement, but opening windows can often cause noise problems. This research develops a window system which allows natural ventilation while reducing noise transmission. The core idea is to create a ventilation path by staggering two layers of glass and using micro-perforated absorbers (MPA) along the path created to reduce noise. The MPA are made from transparent materials so that daylighting is relatively unaffected. Starting with a brief introduction of the MPA theory and its application in ducts, the paper presents a series of numerical simulations using finite element method based software FEMLAB, and experiment results measured between a semi-anechoic chamber and a reverberation chamber. Performance in acoustics, ventilation and daylighting are all taken into account. A basic window configuration is first considered, studying the effectiveness of various window parameters. A number of strategic designs are then examined, including external hoods and louvers in the sound path. There is generally a good agreement between simulation and measurement, and the noise reduction can be as good as a single glazing, with air movement to achieve occupant comfort, rather than just for minimum air exchange. [Work supported by EPSRC.] [ABSTRACT FROM AUTHOR]