Destructive condensation in walls and accelerated deposition of dirt on wallpapers can result from attempts to maintain within a historic building climatic conditions too widely different from those outdoors. More testing and experience are needed in selecting temperature and relative humidity levels that represent the hest compromise between the needs of artifacts and the structural limitations of buildings that contain them. Crumbly old plaster on which wallpaper is found may merit consolidation, and this can be done practically using a variety of organic and inorganic materials. Temporary removal of the paper is almost surely necessary. Plaster that is merely loose from its support can often be reattached without removing the wallpaper. Making new plaster to match old is not difficult, and modifiers can be used to improve properties. Wallpapers that have been mounted directly on wood are attacked by acids from the wood. -- AATA