Materials not related to current research needs nor required for archival purposes are discarded when there are duplicates elsewhere on campus. Multiple copies of outdated monographs are usually not retained. Missing materials are replaced with new editions unless a specific edition is considered by the librarian to be a classic in the field. Titles are selectively preserved if there is available alternative funding. Preservation decisions are made on a case-by-case basis, following the general guidelines established by the Main Library. An increasing percentage of monographs are being purchased as e-books, via package purchases from publishers, and as single titles.