The choice of a range of temperature and relative humidity for the general museum environment must consider a number of factors related to the materials and construction of objects in the collection. These include critical transitions of the materials (such as glass transition and deliquescence points), physical and mechanical properties, chemical reactivity, and the effects of environmental changes within the allowed range. Changes caused by environmental fluctuations can be shown to be generally reversible (non-damaging) within a relatively wide (±10 to 15 per thousand) range in the moderate RH region. A range that is safe for the general collections and minimizes the number of inevitable exceptions can be determined. Other factors such as building design and construction, local climate, energy costs, and available funds and time then can be considered to develop a climate control strategy that maintains the climate within the safe range while conserving energy, funds, and effort.