Although this essential deals with acoustic measurement methods in rooms and buildings, acoustics here is not to be understood as building acoustics. In addition to conventional methods for assessing indoor climate and achieving energy-efficient air conditioning, acoustic methods can provide information useful for indoor climate design, such as:   • Analyzing sound speed distributions as a source of information about temperature and flow fields in rooms, • Acoustic detection of leaks to identify unwanted ventilation or air exchange and thus energy losses.   These methods partly originate from other fields of knowledge, including meteorology, tomography, and acoustic imaging. They can therefore be regarded as alternatives and supplements to conventional methods for energy-efficient indoor climate design.