The libraries of Duke University and the University of North Carolina at Chapel Hill have cooperated in the development of their collections for over fifty years. North Carolina State University in Raleigh became a party to the agreements in 1978 and the University of Virginia participates on a limited basis. The programs are intended to increase the range of research materials available to the libraries’ users and are based on assignments of areas of collecting responsibility at the research level and the avoidance of all unnecessary duplication of library materials. The programs operate through frequent communications among the collection development staffs. This paper describes these programs and makes several general observations on the operation of cooperative collection development programs based on the experience of these libraries.