A computerized research technique for measuring the space utilization of public library facilities provides a behavioral activity and occupancy analysis for library planning purposes. The library space utilization (LSU) methodology demonstrates that significant information about the functional requirements of a library can be measured and displayed in a quantified form. It has primary importance as one of the first applications of ccmputerized research techniques to the field of library facility planning. LSU has been designed to be utilized by library management, library building consultants, and architects. It measures activity or spatial relationships between functional divisions within the library as well as determining occupancy factors for the respective divisions of library staff and the public. The methodology provides a behavioral analysis of the library environment based on actual observation. This information can be cost-effectively displayed in a library's building program to enhance the probability of a more functionally efficient design. LSU is akin to behavioral studies such as tracking studies, time and motion studies, circulation pattern studies, space-time log studies, traffic flow studies and queuing theory studies. (Author/RAA)