The National Union Catalog (NUC) resulted from years of planning by librarians. Its history includes: (1) establishment of exchange agreements in 1909 with continuous increase in size resulting from donations and appropriations; (2) availability in book catalog form in 1946; (3) publication of titles of 1956 and later imprints, useful in acquisitions, interlibrary loans (ILL) and cataloging; (4) compilation of pre-1956 imprints beginning in 1976; and (5) publication of the NUC Register of Additional Locations (RAL) listing title locations not reported earlier. Although NUC production costs have risen and standards control problems exist, LC continues to extend the usefulness of NUC. The RAL will be more readily available in computer output microform to meet ILL and acquisitions needs of librarians. "Name Headings with References," containing new and revised name headings and references for LC catalogs, is an additional cataloging aid. As a result of Cooperative MARC and MARC Online Input System projects, LC is developing a format for machine-readable reports to the NUC with the possible development of online NUC. LC is committed to planning; however, limited time and resources necessitate the determination of priorities. Input from other libraries is imperative in making decisions to meet future needs. (Author/KP)