This journal article describes the deterioration of library and archival collections, particularly books published after 1850. Ancient paper, made from cotton and linen rags, survive today while papers of recent manufacture deteriorate rapidly due to materials (eg. wood pulp, chlorine bleach, alum-rosin sizing) used in processing. Acid hydrolysis occurs in paper at high humidities causing weakness and embrittlement. Solutions to problems of acidic paper include microfilming of pages of little intrinsic value, deacidification (eg. calcium or barium hydroxide neutralized with calcium bicarbonate), and repairs to paper by leafcasting. The diethyl zinc gas method being tested by the General Electric Company at Valley Forge, Pennsylvania would permit economic neutralization of large quantities of books without costly disassembling and rebinding. Future problems could be eliminated by publishing books on alkaline paper. This article is a reference for book conservation and library science.