This handbook is intended for use by the humidification industry. Its purpose is to promote better understanding of terminology, to provide insight into the benefits of humidification, to serve as a guide for humidification requirements in various industrial and building settings, to assist in the selection of appropriate humidification equipment, and to aid in constructing a satisfactory humidification system. After introducing terminology and discussing how humidity is measured, various aspects of humidification's importance are discussed, especially with respect to industrial processes. Humidification in different industries and indoor environments, including library and museums, is then discussed. The remainder of the handbook concerns construction techniques and equipment required to achieve appropriate humidity control.