Reviews the concept of permanence for paper. Although not difficult to describe in general terms, permanence needs to be defined by measurable properties. It is suggested that permanence be defined in terms of resistance to chemical agents and be characterized accordingly. Since experimental data show that papers made by hand before 1800 exhibit excellent chemical permanence, it is proposed that they be designated Type I papers to distinguish them from machine-made products dating to the last 180 years. The treatment of accelerated aging is also discussed with regard to experimental details and the interpretation of results.