Storage conditions play a critical role in determining the useful lifetime of electronic media and more traditional forms of information storage. Successful management of storage environments requires that the effects of temperature and RH conditions on the decay of collections be understood and controlled. The Image Permanence Institute (IPI) has developed algorithms that provide quantitative measures of the risk of three important kinds of decay: mold, dimensional change, and natural aging (spontaneous chemical change in organic objects). These algorithms operate on T and RH readings made over a period of time and provide integrated, single-value metrics of the “preservation quality” of a particular storage environment. IPI has incorporated the algorithms into a software product known as Climate Notebook®. This software is now in use in hundreds of museums and libraries worldwide. The approach has proven to be both practical and useful as a planning and evaluation tool for storage facilities.