Climate control is important for paper based artifacts in terms of preservation. Definitions for climate and relative humidity are given. Moisture in the air comes from different sources and exists at varying levels. The presence of high levels of moisture will encourage some deteriorative processes such as acid formation in paper and bindings, the breakdown of adhesives and mechanical breakdown due to the swelling and shrinking of materials. Temperature and relative humidity ranges and allowable fluctuations are recommended with the goal of maintaining stable conditions throughout the year. Monitoring instruments are suggested with descriptions of their operation, effectiveness and price. Equipment may include thermometers, psychrometers, hygrothermographs and dataloggers. Personnel must be trained to maintain the equipment and to record and interpret the data. In some cases remedial action such as the installation of environmental controls and improved storage should be considered. Equipment sources are included.