The term of copyright has steadily expanded under U.S. law. The first federal copyright legislation, the 1790 Copyright Act, set the maximum term at fourteen years plus a renewal term (subject to certain conditions) of fourteen years. The 1831 Copyright Act doubled the initial term and retained the conditional renewal term, allowing a total of up to forty-two years of protection. Lawmakers doubled the renewal term in 1909, letting copyrights run for up to fifty-six years. The 1976 Copyright Act changed the measure of the default copyright term to life of the author plus fifty years. Recent amendments to the Copyright Act expanded the term yet again, letting it run for the life of the author plus seventy years.
The table above illustrates the growth of the general U.S. copyright term over time, including the retroactive effects of various statutory extensions. Note the overhanging ledges. The 1962-74 Acts, the 1976 Act, and the Sonny Bono Act reached backwards in time, extending the copyright term even for works that had already been created. The Supreme Court has held that legislative trick constitutional, notwithstanding copyright policy’s implied aim of stimulating new authorship—not simply rewarding extant authors.
[NB: The above text comes from part of my draft book, Intellectual Privilege: Copyright, Common Law, and the Common Good. Specifically, it comes from Part I, Chapter 3.A.1: Copyright Imbalance: Duration of Copyright. You can find a complete draft of the full chapter, together with footnotes, here [PDF]. I welcome your comments.]