point of view and requires a well-founded theory based on the fundamental flow equations to ensure reliable results. In the book, a model is set up for a room with two openings to the surroundings and with a uniform indoor temperature. From this basic model, variants are developed for rooms with several openings and/or with a stratified indoor temperature. Further, for each variant, versions are set up where the difference between outdoor and indoor air density, or the difference between the indoor and outdoor temperature, or the net heat input rate is the independent thermal variable. The scope of application is determined, and the opening area ratios are analysed with the aim to obtain optimal ventilation conditions.The book is of interest for building engineers who are or want to specialise in natural ventilation, to under-graduates who wish to have natural ventilation as their special subject, and to postgraduates who work with subjects where it is relevant to involve buoyancy-driven ventilation. For undergraduates in general, especially Chapters 2 and 3 are of interest.