The objective of this study was to determine how large research libraries perform the function of collection development. The paper describes collection development theory within the formal organizational structure of the library, identifies the actual decision points involved in selection of materials, and examines the staff and facilities provided for collection development. Information was obtained through personal interviews of 300 librarians at 18 ARL (Association of Research Libraries) libraries throughout the U.S. Those interviewed included collection development officers, area and subject librarians, bibliographers, and curators. Findings are summarized in the following areas: allocation decisions, automation, approval plans and blanket orders, book funds, collection policies and committees, cooperation, elitism vs. no one cares, evaluation of collections, exchanges and gifts, faculty vs. librarians in selection, interlibrary loans, microforms, organization, preservation, reference, retrospective, serials, space and staff, teaching, technical services involvement, use studies, and weeding and storage. (Author/JAB)