A reference for all those who need to select the correct moisture level in a variety of building types. As building services develop, buildings become more independent of outdoor climate. Moisture plays a critical but subtle role in our everyday lives, but knowledge of the influence of moisture on a variety of phenomena is fragmented. Causes and results of poor humidity selection are explained, and full reference lists are provided. It is a companion to the "Handbook of Dehumidification Technology", by the same author, and explains why this control is so important. It may be useful to building services engineers, surveyors and architects as well as civil, electrical and chemical engineers.