Functional definitions of all work performed by the University of California (UC) libraries is presented. The work of the total system has been divided into 21 major functional areas called subsystems and these have been further subdivided into 71 more specific functional segments called modules. Existing organizational structure of the UC libraries varies greatly and the functional definitions are independent of these variations. Similarly, each segment of the system is defined to deal with all types of library materials so that the definitions are independent of material categories. Finally, the definitions were developed with a minimum emphasis on current manual or possible future mechanized means for performing the functions. (Other documents on this program are: LI 003640 and 003642.) (Author)