This study examines holdings of 21 members of the Association of Research Libraries for books reviewed in American Historical Review. The study asserts that approval plans are inadequate for collecting from small publishers or from scholarship that crosses disciplinary boundaries. Although approval plans increase efficiency in collection development, the need for expert selection cannot be overstated. Results indicated that small publisher’s books were less likely to be in libraries than university press publisher’s books, and that history monographs are frequently classified outside disciplinary boundaries, and are therefore invisible to approval plans that define disciplines based on classification systems.