Copyright is a limited, statutory monopoly granted to creators of “original works of authorship fixed in any tangible medium of expression.” It comes into effect automatically at the time the work is created.
Copyright law governs more than just copying. It establishes the rights that creators have in relation to their works, as well as the rights others may have to reproduce, distribute, modify, display, or perform them. Copyright is best understood as a bundle of rights, each of which may be exercised independently.
Copyright exists to “promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors exclusive Right to their respective Writings and Discoveries.”
U.S. Constitution, art. 1, sec. 8
“The primary objective of copyright is not to reward the labor of authors, but to promote the Progress of Science and useful Arts. To this end, copyright assures authors the right to their original expression, but encourages others to build freely upon the ideas and information conveyed by a work. This result is neither unfair nor unfortunate. It is the means by which copyright advances the progress of science and art.”
Supreme Court Justice Sandra Day O’Connor
“The constitutional purpose of copyright is to facilitate the flow of ideas in the interest of learning. The primary objective of our copyright law is not to reward the author, but rather secure for the public the benefits from creations of authors.”
U.S. House Report, Berne Convention Implementation Act of 1988
Because of international treaties the U.S. has signed, works created or published in countries other than the United States are subject to U.S. copyright law when used in the United States.
Generally speaking, copyright lasts for the life of the author or creator, plus seventy years. Once this time is passed, works are said to enter the “public domain.” For more information, see section 6 of this guide, “When Works Pass into the Public Domain.”
The copyright adhering to a work is not the same as ownership of a particular copy of that work. For example, if you own a musical recording you may sell or give it away, but you may not copy it unless your copying can be justified by an exemption granted in the law.
Respecting copyright is not the same as giving proper attribution to the author or creator of a work you use. For example, it may be a violation of copyright to post on your website some material (text, image, etc.) that you copied from elsewhere on the internet, even if your posting clearly states the source of that material.
Licensed works are governed by contract law. Contract law generally supersedes the provisions of copyright law and may give users more or fewer rights than the copyright law does.
 Quoted in Carrie Russell, “Current Copyright Issues Facing Academic Librarians,” a seminar offered by the American Library Association, 2004.