Copyright law in the U.S. is governed by federal statute, namely the Copyright Act of 1976. The Copyright Act prevents the unauthorized copying of a work of authorship. However, only the copying of the work is prohibited--anyone may copy the ideas contained within a work. For example, a copyright could cover a written description of a machine, but the actual machine itself is not covered. Thus, no one could copy the written description, while anyone could use the description to build the described machine.
Copyrights can be registered in the Copyright Office in the Library of Congress, but newly created works do not need to be registered. In fact, it is no longer necessary to even place a copyright notice on a work for it to be protected by copyright law. However, the Copyright Act does provide additional benefits to those who register with the Copyright Office. Consequently, copyright registration and the use of a copyright notice is recommended.
In addition to these descriptions of copyright law, BitLaw contains additional resources relating to copyrights: