Recent developments at the Canadian Conservation Institute (CCI) in the area of relative humidity (RH) control are discussed. This includes two novel methods of RH control for museums, art galleries, and historic houses: humidistatic controlled heating and a relative humidity control module for display cases. The operation and performance of each system are explained, and results of field trials are presented. The issue of air leakage in display cases is discussed with emphasis on the factors determining the leakiness of a case. See also AATA 19-919 for related study.