Copyright is controlled by laws passed by Congress, cases heard through the judicial system as well as international treaties that Congress has entered into with other nations such as the Berne Convention.
These laws also attempt to define copyright infringement. The core concept of infringement is using someone else's protected work without their permission. Oftentimes the word infringement is associated with terms such as piracy, illegal downloading or file sharing, bootlegging or simply theft. That portion of the Copyright Act discussing infringement including civil penalties, damages and potential criminal prosectution can be found here.
A collection of various nations copyright laws can be found at the United Nations UNESCO International Copyright Law Collection.
Check these links for more information on the TEACH Act.
The TEACH Act requires that distance learning institutions provide notice to students that materials used in connection with the course may be protected by copyright.
There are a number of exemptions under the TEACH Act that allow for the use of copyrighted materials that would otherwise be considered infringing.
Additional Information on the TEACH Act can be found at the following sites:
Want to make sure your class is TEACH Act compliant? Try this TEACH Act checklist.
Learn more about The Digital Millennium Copyright Act at this American Library Association guide.
Wikipedia Entry on DMCA.
Update for 2012 on DMCA for Electronic Frontiers Foundation.