"Circulars are published by the Copyright Office to provide up-to-date and authoritative information to a general audience. Circulars are arranged below by topic and cover the basics and fundamental concepts of copyright law, highlights of policies and procedures of the Copyright Office, and registration issues for specific categories of works. For full details regarding the Office's policies and procedures, refer to the Compendium of U.S. Copyright Office Practices, third edition."
Please note: in September 2017, the Office began releasing refreshed and updated circulars. A complete guide to circular updates can be found here<https://www.copyright.gov/circs/circular-update-guide.pdf>.