If you’re an author, this is important.
From their site: “A Library of Congress catalog control number is a unique identification number that the Library of Congress assigns to the catalog record created for each book in its cataloged collections. Librarians use it to locate a specific Library of Congress catalog record in the national databases and to order catalog cards from the Library of Congress or from commercial suppliers. The purpose of the Preassigned Control Number (PCN) program is to enable the Library of Congress to assign control numbers in advance of publication to those titles that may be added to the Library’s collections.”
Each book should have these if you ever want to get your book in a library, etc.
The following is an official email directly from them to publishers (and self-publishing authors).
Thanks for your patience as we have been preparing our new pre-publication tool for the book publishing community, PrePub Book Link from the Library of Congress. The new tool will bring the Library’s Cataloging in Publication (CIP) and Preassigned Control Number (PCN) programs together in a unified, easy-to-use web-based tool.
We’ve made the decision to delay the launch of PrePub Book Link until spring of 2019, in order to make sure we roll out the best possible new tool to make your workflow easier, whether you’re an author, a publisher, or a CIP partner institution.
The Library will provide user guides for PrePub Book Link to ease the transition to this powerful new tool. You’ll receive additional emails with more details and specific launch date this spring.
Look forward to Library of Congress PrePub Book Link, coming in the spring of 2019.
CIP and Dewey Section Head and Program Manager
U.S. Program, Law & Literature Division
Acquisitions & Bibliographic Access Directorate
Library of Congress