Copying in Patent Law

59 Pages Posted: 19 Sep 2008 Last revised: 6 Feb 2011


Patent law is virtually alone in intellectual property (IP) in punishing independent development. To infringe a copyright or trade secret, defendants must copy the protected IP from the plaintiff, directly or indirectly. But patent infringement requires only that the defendant's product falls within the scope of the patent claims. Not only doesn't the defendant need to intend to infringe, but the defendant may be entirely unaware of the patent or the patentee and still face liability.

Nonetheless, copying does play a role in some subsidiary patent doctrines. For example, the question of whether patent damages should be set in order to deter infringement depends critically on whether infringers are in fact aware they are infringing, or at least that they are using the plaintiff's technology. Copying - or at least intent to infringe - is also an element of claims for indirect infringement. The definition of "willful infringement" also turns on the question of culpability, at least in the popular understanding of that term. More significantly, the rhetoric of patent law (and of IP law more generally) often seems to presuppose that defendants in patent cases are in fact engaged in copying. Similarly, the outcome of public policy debates over patent reform may well turn on the perception of patent infringers as either bad actors or as innocent businesspeople who accidentally ran afoul of a patent.

Unfortunately, no one seems to know whether patent infringement defendants are in fact unscrupulous copyists or independent developers. In this paper, we seek to answer that question. Because copying is not an element of any patent cause of action, courts do not normally make explicit findings as to whether defendants have copied. Instead, we turn to a variety of proxies to try to identify the subset of cases in which copying is alleged or proven. We look both at the allegations made in a random sample of complaints and at the treatment of copying in recent reported decisions. We find that a surprisingly small percentage of patent cases involve even allegations of copying, much less proof of copying. Copying in patent law seems to be the exception, not the rule.

Suggested Citation

Cotropia, Christopher Anthony and Lemley, Mark A., Copying in Patent Law. North Carolina Law Review, Vol. 87, p. 1421, 2009, Stanford Public Law Working Paper No. 1270160, Available at SSRN:

Christopher Anthony Cotropia

University of Richmond - School of Law ( email )

28 Westhampton Way
Richmond, VA 23173
United States

Mark A. Lemley (Contact Author)

Stanford Law School ( email )

559 Nathan Abbott Way
Stanford, CA 94305-8610
United States

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