[en] Six-digit subject category numbers are used in the storage, retrieval, and manipulation of bibliographic information entered into DOE's computerized bibliographic information system. These numbers are used in the preparation of printed documents, such as bibliographies and abstract journals, and as searching aids in the on-line system, RECON. The meaning attached to each of these numbers is explained in this document. It was prepared for use by those individuals responsible for the assignment of category numbers to documents being entered into the TIC system, those individuals and organizations processing magnetic tape copies of the files, and others who, having no access to RECON, have need for printed copy