If the energy losses due to ventilation have obviously become an important problem since the energy crisis, there is still a lot to be done with respect to the behaviours. Previous research has given results about the share of venti lation losses i n the energy balance, and the rational reasons to introduce fresh air into the house. Annex VIII is specialized in the attitudes of the inhabitants, in their habits with regard to ventilation and even in their apparent irrationality. That should lead to know whether the ventilation behaviour of the inhabitants can be modified and to estimate the amount of energy savings which might result therefrom. To reach these final goals, the Annex VIII foresees three levels. The first one will tempt to describe how people behave with regard to ventilation, the second level will try to find the reasons of such a behaviour, and the third level will estimate the amount of energy loss due to this behaviour. A t the present time, some countries have already carried out one or several steps of the Annex, but it is still too early to go deeply into the conclusions. A behaviour as plain as open a window, but so important with regard to energy still stays partly an unknown.