The purpose of this report is to summarise the work of IEA Annex 18 on demand controlled ventilation. It is primarily aimed at building services practitioners, designers and policy makers who require background knowledge of the operational principles and range of applicability of this approach to ventilation. The primary focus is on applications and the conditions required for the operation of such systems. This international activity has been carried out by a working group of researchers from ten countries (Appendix 1) with Sweden bearing the main responsibility as Operating Agent. More detail is available in a set of project reports, as summarised in Appendix 2.