Discusses the kinetics of aging and its implications for the evaluation of changes in the aging process, especially as applied to accelerated aging. The problem of comparing accelerated aging conditions is shown to be separate from that of evaluating changes occurring under one specific set of conditions. Thus tests and measurements that can be used to evaluate the results of a specific accelerated aging experiment are not necessarily valid for use in determining whether two sets of aging conditions is comparable to, or accurately simulates, natural aging. The criteria for comparing two sets of aging conditions are defined and applied to the problem of evaluating accelerated aging conditions. Data from the analysis of individual reaction products of artificially aged paper samples are used to determine the effects of temperature and relative humidity (RH) on the rates of individual reactions. Changes in the distribution of reaction products are used as indicators of changes in the aging process. The aging process of cellulose under the conditions studied (60-90°C, 30-80% RH) is shown to be RH dependent, but relatively temperature independent. Thus raising the temperature at constant RH speeds up the aging process without significantly altering it. If the RH is changed, then the aging process is altered and equivalent states of aging cannot be reached. Accelerated aging should be conducted at the same relative humidity as the conditions to which the results are to be applied. The data also indicate that lowering the relative humidity from 50% to 30% slows the rate of hydrolysis by a factor of three to five. -- AATA