MARC (MAchine-Readable Cataloging) is a data format that emerged from a Library of Congress initiative to allow computers to exchange, use, and interpret bibliographic information. It provides the mechanism by which most library catalogs are built today. A MARC record uses tags, indicators, and subfields to organize bibliographic data in a structured format that computers can process. Common fields include title (245), author (100), subject headings (650), and notes (500). The Network Development and MARC Standards Office at the Library of Congress maintains and develops the MARC standards.