LCCN is an acronym for Library of Congress (LOC) Control Number, a cataloging number assigned to books in the LOC collection. The LCCN is obtained prior to a book’s publication through the Preassigned Control Number (PCN) program. Only US publishers are eligible to participate in the PCN program. When a book is nearly ready to print, the publisher applies for the PCN (eBooks, most books under 50 pages, and certain other book types are not eligible for this program). Once received, the number is added to the book’s copyright page (preceded by “Library of Congress Control Number:”).

After the book is printed, one copy of the book must be sent to the LOC’s Cataloging in Publication (CIP) Division. Assignment of a PCN/LCCN and submission of a book to the CIP Division does not guarantee the book will be added to the LOC collection. From the LOC website:

Final determination of works selected and cataloged is made by selection librarians and recommending officers in compliance with Library of Congress collection development policies upon receipt of the printed book. Please note that while a title may receive a preassigned LCCN, the Library of Congress is under no obligation to provide preliminary or final cataloging information within its catalog for titles that are not ultimately selected for the Library’s permanent collection.

Accepted books are assigned data such as a call number and subject/category headings. They are listed in the Library of Congress Online Catalog and the book copy submitted is placed in the LOC holdings.