The problem of selecting which sites to use in locating library and information centers in order to best achieve system objectives is modeled as a mixed zero-one linear programming problem and examined in detail. The model incorporates an objective function based on the costs of locating centers and of transmitting information to the users. The model also incorporates constraints to account for the scarcity of service available at the various sites (capacity) and for the need to at least satisfy the minimal demands of the users. The model is meant to be used to aid the library system's management in making better location decisions, since the objective function can be shown to reflect the evaluation of the library as an information retrieval system and as a service organization. Moreover, the model is seen to be related to the problems of locating plants and warehouses. A reformulation incorporating the properties of both interlibrary communication networks and the transmission of information services to clients is presented and discussed. The dual problem is derived and analyzed to yield several economic implications of the locational model for librarians. (Author)