A copyright represents a legal monopoly on the right to reproduce, sell, publicly display, publicly perform, adapt or license a work of authorship. The author of a work might not be the copyright holder -- musical artists, for example, typically sell their copyrights to a recording company. A copyright doesn't have to be registered with the U.S. Copyright Office to enjoy protection -- it attaches as soon as the work is reduced to tangible form. If you wish to use someone else's song, you will need to obtain a license.
Search for the copyright owner using the online search engine on the website of the U.S. Copyright Office. Since this database only includes works that were registered or recorded by the U.S. Copyright Office, you must continue your search elsewhere if the search engine offers no listing.
Examine a published copy of the work to identify the copyright holder. Many copyrighted works contain copyright notices on every published copy -- the sleeve of a DVD, for example. Copyright notices include the name of the copyright holder at the time of publication. Copyright notices are not universal, however, because under U.S. copyright law, works published after March 1, 1989 don't need notices to ensure copyright protection.
Contact the artist to find the name of the current copyright holder, if you know the author's name and the work contains no copyright notice.
Search the databases of copyright collectives such as the Copyright Clearance Center. A copyright collective can help you locate the copyright holder using, for example, the name of the song. If you know the copyright holder's name, a collective can provide you with contact details.
Determine what type of license you are seeking. A blanket license allows you access to many songs (even with different copyright holders) for a flat annual fee. A synchronization license allows you to use a song together with visual media such as a TV commercial, and to re-record it if necessary. A master recording license allows you to use a recorded song in a visual media composition. A mechanical license allows you to reproduce a recorded song by, for example, creating a cover version. A performance license allows you to perform a song at live performances or presentations, or play it on a CD for a live audience. A print license allows you to copy or print lyrics or written music.
Contact the copyright holder to identify the appropriate licensing authority. This depends on the type of copyright license you are seeking and the identity of the copyright holder. The appropriate authority may be the copyright holder, a record label, a performing rights organization or a collective society. The American Society of Composers, Authors and Publishers, for example, offers performance licenses for millions of songs, while the Harry Fox Agency offers mechanical licenses for millions more.
Contact the appropriate licensing authority for permission to use the song. You should identify yourself and provide your contact details, clearly describe the work you want to use, state why you wish to use the work, and state exactly how you intend to it -- where, when and for how long.
Negotiate a written copyright licensing agreement with the appropriate party -- a performing rights organization, for example, the copyright holder or the record label. The agreement should clearly identify you, the copyright owner and the copyrighted work. It should also specify the type of license granted as well as any time, place and duration of use and any geographical restrictions. You will probably have to pay either royalties (a percentage of sales) or a flat fee. The cost of the license will depend on the type of license you seek and the extent of your use.