Adopted from Basics from the US Copyright Office
Why is copyright law important? Copyright law has a dual role. It provides exclusive rights to authors in order to protect their work for a limited period of time but it was also established to promote creativity and learning.
When does a work become copyrighted? ...when it is fixed* in a tangible medium of expression. After March 1, 1989 works no longer require a copyright notice (© or the word copyright, the author´s name and the year of publication). Copyright registration is also no longer required. However, it is wise to affix a copyright notice to works so that the owner of the copyright can be easily identified.
What are the copyright holder's exclusive rights? The owner of a copyright has six exclusive rights: To reproduce the work. To distribute the work. To create derivative works*. To publicly perform* the work. To publicly display* the work. To publicly perform sound recordings by means of a digital audio transmission.
How long does copyright last? Works created on or after January 1, 1978 are protected for a term of the life of the author plus 70 years. If it is a corporate author then the protection is for the shorter of 95 years from publication* or 120 years from creation*. Works created and published prior to 1978 may be protected for different lengths of time. For more information regarding the length of a copyright, please see the copyright duration chart.
What is the public domain? The public domain consists of all works that never had copyright protection and works that no longer have copyright protection. The public domain also includes most works created by the United States government. All works in the public domain are free for the public to use. Works published in the United States prior to 1923 are in the public domain.
For information on copyright term lengths and the public domain, see Cornell University's guide.