The aging of books depends upon five factors: the kinds of paper fibers used; storage conditions of the library collection; causes of paper deterioration; the amount of acid attack; and methods of deacidification. The structural components of the paper pulp are explained, and the causes of deterioration briefly mentioned. By examining books from several libraries under different external environmental conditions (i.e, New York City, Chicago, and Appleton, WI), conclusions were reached regarding the life of a book and the ambient air pollution. Deacidification is needed in library collections and especially in those collections in urban areas. Storage conditions must be designed to maintain a neutral condition. Specific methods of deacidification are discussed at length.