The model circulation system outlined is an on-line real time system in which the circulation file is created from the shelf list and the terminal inquiry system includes the capability to query and browse through the bibliographic system and the circulation subsystem together to determine the availability for circulation of specific documents, or documents in a given subject area, or by a certain author, etc. The system is designed independent of the input medium. The user does not have to be present to borrow an item. The model goes beyond the operational limits of most existing circulation systems and can be considered a reflection of the current state of the art. Four types of circulation systems are discussed in order to measure the capabilities of these systems against the model and each other. The four systems are: (1) manual, (2) semi-automated (non-computer), (3) data collection (batch) and (4) on-line. (NH)