Library administrators, faced with the problems of acid-paper deterioration, are examining mass deacidification procedures. Mass deacidification of acidic books while they are still physically sound and not yet brittle is the most cost-effective corrective action to extend the life of the paper. There are currently at least five mass deacidification processes available or under development, so that library administrators can begin to plan for the process. A brief and nontechnical description is given of the following five techniques: (1) DEZ (diethyl zinc), a process at the pilot stage; (2) Wei T'o, a liquified gas process that is in use in at least two locations; (3) BPA, the Book Preservation Associates System, currently available in New Jersey; (4) Bookkeeper, a process under development that involves magnesium oxide; and (5) the Lithco process, in the pilot stage. A table summarizes the properties, selection requirements, cycle times, and development stages of each of these processes. Considerations of process use, such as length of time required to treat a collection, potential damage or strengthening effects, and evaluation issues are reviewed. (Contains 103 references.) (SLD)