The copyright law of the United States grants monopoly protection for "original works of authorship". With the stated purpose to promote art and culture, copyright law assigns a set of exclusive rights to authors: to make and sell copies of their works, to create derivative works, and to perform or display their works publicly. These exclusive rights are subject to a time limit, and generally expire 70 years after the author's death or 95 years after publication. In the United States, works published before January 1, 1928, are in the public domain.
United States copyright law was last generally revised by the Copyright Act of 1976, codified in Title 17 of the United States Code. The United States Constitution explicitly grants Congress the power to create copyright law under Article 1, Section 8, Clause 8, known as the Copyright Clause. Under the Copyright Clause, Congress has the power "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."