The National Union Catalog Pre-1956 Imprints (NUC) is an unique bibliographic resource. The NUC's 754 volumes were created before automation, before national databases, and before the Internet. 

The National Union Catalog is a national card catalog of books held by major American libraries. 

As an effort that ran from 1968 to 1981, it reflects what libraries held when it was created. Finding a record in the NUC does not guarantee that libraries still own it. Once a book has been located, UD faculty, staff, and students may request it via Interlibrary Loan. Rare and historical books may not be eligible for interlibrary loan.

The central concept in using the NUC is main entry, which is usually, the author or editor of a work. Occasionally, a title or publisher is the main entry. If this is the case, the NUC will refer the reader to another entry. 

Note that capitalization and abbreviations are not always in compliance with modern usage. 

Sample Entries		Explanation
		In this entry, William Maxwell (1784-1857) wrote an address which was included in the book that Alfred James Morrison edited. To identify what libraries may own this, look it up under "Morrison, Alfred James, 1876 -"   In this entry, William Maxwell (1784-1857) was the editor of the Virginia Historical Register. To identify what libraries  may own this item, look it up under "Virginia historical register." This entry is a main entry in the NUC. William Maxwell (1908- ) wrote a book called Bright Center of Heaven, published by Harper & Brothers in 1934. NM indicates the NUC Pre-56 accession number. PZ3.M4524Br is the Library of Congress Call number for this book. 34-28619 is the Library of Congress Card Number (LCCN) of this book. This can be useful in checking the OCLC system for up to date holdings about this book. NUC and OCLC work together to provide citations to older books. DLC CtY TxU OCU OCl & NN are abbreviations of libraries that may own this book. Abbreviations are listed on the binding pages in the front and back of each volume, first by state, and then by institution. DLC is the Library of Congress  CtY is Yale University TxU is the University of Texas, Austin OCU is the University of Cincinnati OCl is Cleveland Public Library NN is the New York Public Library