The United States is the only country in the world that awards patents to the first person to invent something, rather than the first to file a patent application. In order to determine who is first to invent, the United States has created an elaborate set of "interference" proceedings and legal standards to define invention and decide how it may be proven. Supporters of this system claim that it is necessary to protect small inventors, who may not have the resources to file patent applications quickly, and may therefore lose a patent race to large companies who invented after they did. Advocates of global patent harmonization have suggested, however, that the first inventor is usually also the first to file, and that the first-to-invent standard is unnecessary and wasteful.

In this Article, we study U.S. Patent and Trademark Office ("PTO") interference proceedings and court cases in which the parties dispute who is first to invent. We find that the first person to file is usually, but by no means always, also the first to invent. In over 40% of the cases, the first to invent is last to file. We also find that the long-standing rule that discriminated against foreign inventors by requiring proof of inventive activity in the U.S. had surprisingly little effect on outcomes; that a large number of priority disputes involve near-simultaneous invention; and that the vast majority of such disputes could be resolved without reliance on much of the evidence the law permits. Finally, we study the role of small inventors to see whether they are disproportionately the beneficiaries of the first to invent system. While the evidence is mixed, it does not appear that small inventors particularly benefit from the first to invent system.

Part I describes the legal background for the international debate over how to determine patent priority. Part II describes our studies and discusses our results in detail. Finally, Part III draws conclusions for policy-makers from the data. There is some truth to the arguments of both sides in this debate. The first to invent system does produce significantly different results in individual cases than a first to file system would. But it is not clear that those different results are particularly fairer, or that they are worth the cost. We suggest some possible ways to modify the U.S. system to take account of these facts without changing entirely to a first-to-file system.