The recent situation on developments in an expanding field of reference and information service is reviewed through the cooperative arrangements and comprehensive planning among libraries in America. The growth of reference cooperation is examined first along with the social forces that influenced the library interdependence for service. Of the various interlibrary programs identified in relation to the cooperative reference work, interlibrary loan is viewed as the key to the use of library resources based on equal access and making use of the tools for information and research, therefore a reference principle. Several kinds of library systems specifically intended to improve the reference situation are identified and described in detail without any attempt to evaluate their performance in terms of unit size, cost, or quality of the service.