The existing methods of protecting cellulose from acid attack are reviewed. These methods are unsuitable to preserve paper and books or are prohibitively expensive. The suggested new practice consists of impregnating paper and books with a nonaqueous solution containing an organic solvent and a benign alkaline deacidification agent. The solution may be applied by immersion, spraying, or brushing. Magnesium methoxide is the preferred deacidification agent. The feasibility of treating library collections is described.