Historically Significant U.S. Copyright Legislation

Statute of Anne (1710)
The Statute of Anne (named for the queen during which the act was passed) is generally considered to represent the birth of copyright law. The provisions in the act allowed for the exclusive right to print works for a period of fourteen years (twenty-one if the work had already been published at the time of the act’s passage), with the option of an additional fourteen year term should the author still be living. The penalty for infringement was set at one penny per page—half of which could be claimed by the complainant and the other half being given to the Crown—as well as forfeiture of the offending copies. The statute required registering the title of the work with the Company of Stationers in order for the copyright to be binding. Though it does not specifically provide for fair use, the statute does set a legal precedent of sorts for the fair use defense by limiting the power of the rights holders to monopolize the work. Section IV of the statute provides that should printers or booksellers set a price for a book that “shall be conceived by any person or persons to be too high and unreasonable,” that the latter may appeal the price to one of several representatives of the Crown, which have the power to set a fair price.
Complete text (The Avalon Project)

Copyright act of 1790
The United States Congress first adopted laws to protect the rights of authors in 1790. The act, approved on May 31, 1790 and signed by President Washington, inherited many of the provisions of the Statute of Anne, including the fourteen year term with the option to extend for fourteen years. The statute also includes the requirement that the title be registered in order to claim protection. The 1790 statute removes the right of citizens to appeal an unreasonable price. It does, however, extend protection to other materials than books, namely charts and maps. Significantly, the act also includes the requirement that the author be able to claim citizenship in the United States.
Complete text in PDF (U.S. Copyright Office)

Copyright revision 1831
Enacted on February 3, 1831, this act, for the first time, includes musical compositions in the list of protected materials, along with books, maps, charts, prints, cuts and engravings. The revised statute allows for copyright in both unpublished and published musical compositions. In addition, the initial copyright term is extended to 28 years. The 1831 revision also includes the phrase “in whole or in part,” which had been added in 1802. With reproduction of even portions of works controlled, the need for a concept of fair use became apparent. (see Folsom v. Marsh (1841).)
Complete text (Library of Congress)

Copyright revision 1909
The third major revision to the United States copyright took effect on July 1, 1909. The law is still highly relevant, since the copyright in most works published before 1978 is governed by the 1909 act. The law increased the renewal term to 28 years, for a maximum term of 56 years. Significantly for music, the law extended the exclusive right to for-profit performances to music, and introduced the compulsory mechanical license. Under the 1909 law, the copyright term was determined by the date of first publication with the required notice.
Complete text in PDF (U.S. Copyright Office)
Copyright revision 1976
The first major revision in nearly 70 years included several provisions bringing the United States into compliance with the Berne Convention of 1886 (which the United States had previously refused to sign). Among the most significant changes were the elimination of required formalities, such as notice, registration and renewal, and a copyright term based on the lifespan of the author rather than the date of creation. Additionally, the Congress introduced significant copyright exemptions for libraries and, for the first time, formally codified the fair use defense.
Digital Millennium Copyright Act (DMCA) (1998)
Passed in response to the WIPO Copyright Treaty, the act most significantly introduces anti-circumvention measures into the copyright law. The law remains extremely controversial, in part because of the potential it creates for preventing otherwise lawful uses of materials through rights management software and encryption. The Librarian of Congress was charged with examining the DMCA periodically and recommending exemptions as appropriate.
Complete text in PDF (U.S. Copyright Office)

See also: 17 USC §1201. Report on circumvention exemptions.

Technology, Education and Copyright Harmonization Act (TEACH) (2002)
The TEACH act of 2002 amended section 110 of the copyright code to afford additional exemptions for long-distance educational environments.
Complete text (U.S. Copyright Office)

See also: 17 USC §110