The Library of Congress Control Number is one of those publishing terms that sounds intimidating but is actually straightforward once you understand what it does and who needs one.

An LCCN is a unique identification number assigned by the Library of Congress to records in its catalog. It is not a copyright registration, and it does not replace an ISBN. Its primary purpose is to help libraries across the United States catalog and locate your book within the Library of Congress system and, by extension, in library networks nationwide.

The LCCN is assigned through the Preassigned Control Number (PCN) program. Preassigned is the key word — you must apply before your book is published. The Library of Congress reviews applications and assigns numbers to titles that meet their criteria. After publication, you are expected to send a complimentary copy of your book to the Library of Congress as part of the program.

Who should apply? If your book has potential library appeal — nonfiction, literary fiction, reference material, educational content, or anything that libraries might want to stock — an LCCN can make it easier for librarians to find and catalog your title. It signals a level of professionalism and legitimacy that some librarians look for when evaluating acquisitions.

Who can skip it? If you are publishing a short ebook, a niche genre romance intended primarily for Kindle Unlimited, or a workbook with limited library appeal, an LCCN is unlikely to add value. The program is free, but it requires advance planning and a commitment to send a physical copy of your book to the Library of Congress.

The application process is online through the Library of Congress PCN website (pcn.loc.gov). You will need to provide your book’s title, author, publisher information, ISBN, and expected publication date. Processing times vary, but the Library of Congress recommends applying well in advance of your publication date — ideally several weeks to a few months ahead.

A few important details:

• The PCN program is open to publishers of all sizes, including self-published authors
• The Library of Congress reserves the right to decline titles that do not meet their collection criteria
• Mass-produced low-content books, pamphlets under 50 pages, and periodicals are generally not accepted
• Your book must have a U.S. publisher address

The LCCN is printed on the copyright page of your book, typically below the ISBN and copyright notice. If you are using a print-on-demand service like KDP or IngramSpark, you can add the LCCN to your interior file before uploading.

Having an LCCN does not guarantee that libraries will purchase your book, but it removes one barrier to discovery. For authors serious about library placement, it is a free and worthwhile step.

• Library of Congress PCN Program (pcn.loc.gov)
• Library of Congress: About the Preassigned Control Number Program