What do Pretty Woman, National Lampoon's Animal House, and The Godfather have in common? Sure, they're all great movies. But each also contained music in the public domain.

What is the Public Domain?

It's any creative work without copyright protection. You can use public domain material any way you want, and you don't have to get anyone's permission to do so. And best of all, everything in the public domain can be used for free. Most public domain works had copyrights that expired. In addition, all publications created by the U.S. government such as the latest version of the CIA World Factbook are automatically in the public domain.

How can you tell if a Certain Work is in the Public Domain?

First, find out the author and publication date of the work in question. Next, use the following as a guide.

• Works created after January 1, 1978

You'll have to wait awhile for these to enter the public domain. Their copyright term is the lifetime of the author plus another 70 years.

• Works created before January 1, 1978 but not published

If the work was still unpublished by 12/31/2002, it has a copyright term of the author's lifetime plus 70 years. If the work is published or registered by 12/31/2002, it received automatic protection until 2047, in addition to a copyright term of the author's lifetime plus 70 years.

• Works Published from 1964 - 1977

These have an original copyright of 28 years. But instead of falling into the public domain, they automatically received 67 more years of protection.

• Works Published from 1923 - 1963

These also had 28 years of original copyright protection. But they only received another 67 years if the author decided to renew the copyright.

• Works Published before 1923

These works are most likely in the public domain and can be used free of charge. But a little caveat: some foreign works were pulled out of the public domain by a series of recent trade agreements. Therefore, make sure you investigate the availability of such a work before using it.