What is the "prior art" in a patent application?

If you’ve ever worked with patent applications, you’ve probably heard the term “prior art” before. While technically defined in the statute, 35 USC § 102, it’s not exactly light reading, and there are several nuances worth mentioning.

Basically, prior art is the entire database of human knowledge publicly available before the patent application was filed, and describing similar devices, methods, or compositions as the invention itself. It also includes products publicly used or sold, and previously-filed applications (as long as they eventually publish).

During review of the patent application, the USPTO Examiner will spend much of their time searching this vast space for specific references that might prove the invention is not new, or is merely an obvious variation of things already known. These rejections are usually the main roadblocks to obtaining a patent.

Although prior art can technically have any form, it’s almost always either (a) older patents and patent applications, or (b) scientific papers (even if they’re behind a paywall).

Prior art can be obscure: courts have found one copy of a 1970s PhD thesis, available in only a single library in Germany, to constitute prior art. It doesn’t even have to be in English. The key is accessibility of the document to someone looking for it. The Examiner will always provide a full-text copy of any reference, along with a machine translation if necessary.

Prior art also doesn’t require that a physical embodiment of the invention was ever made; a description can often suffice. In fact, it’s normal for the USPTO to find one paper showing some elements of the invention, another paper showing the other elements, and argue the invention would have been obvious from combining the knowledge of the two papers.

Having a full grasp of the prior art is usually impossible. Nevertheless, having a basic understanding of what’s out there can be crucial to having a smooth experience at the USPTO—getting from application to granted patent with the least amount of cost and time.