The application of systems engineering and operations research to the problems of libraries has developed quite strongly during the past five years. The purpose of this paper is to draw attention to this relatively new area. There are serious problems of applying systems engineering to libraries. This is to be expected in the case of a non-profit-making situation where the end product is an intellectual rather than a physical one. Furthermore, although librarians do commonly have an academic orientation, this is usually in the humanities rather than science or engineering. This is quite clearly reflected in library research which commonly includes substantial data collection but no models or hypotheses. Nevertheless, the past few years have seen a significant development in the application of systems engineering to library problems. The achievement, though real, is still quite limited--especially where the behavioral aspects of library use are concerned. There is, in library systems engineering, a need and a challenge. (Author/SJ)