What do the different Library of Congress numbers mean?
There are several Library of Congress numbers which users often conflate. They are: Library of Congress Control Number (LCCN) A Library of Congress Control Number (LCCN) 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 Library of Congress assigns this number while the book is being cataloged. Under certain circumstances, however, a card number can be assigned before the book is published through the Preassigned Control Number Program. What is now known as the Library of Congress Control Number was originally known as the Library of Congress Card Number until the advent of machine-readable records for book materials in the late 1960s. An LCCN can have one of two different structures, based on when it was a
