Prior art is a term used in the patent world.

A patent cannot claim something that is obvious or which already exists. Prior art is an earlier publication, which shows that the invention already exists and so cannot be patented.

What consists prior art varies slightly between different patent offices. The European Patent Office (EPO) rules are relatively simple: to be novel, an invention must not form part of the state of the art on the date the European patent is filed (or the priority data).

To quote the EPO:

Prior art is any evidence that your invention is aready known.  Prior art does not need to exist physically or be commercially available. It is enough that someone, somewhere, sometime previously has described or shown or made something that contains a use of technology that is very similar to your invention.

US rules are a bit more complex, but in general any printed publication that is available to the public is prior art. This includes electronic publication. A product sold or offered for sale in the US also counts as prior art. In some cases, prior art has to be at least a year old to prevent a patent application in the US.

Prior art is not always easy to find. To quote a USPTO paper:

It can be extremely difficult to identify business methods that may have been common practice or common knowledge in an industry, but have not been documented properly, nor dated, nor disclosed in a form that is easily accessible by patent examiners.

For the purposes of assessment prior art, there are two obvious kinds of prior art:

Publication

A publication describing a past assessment innovation is good evidence for prior art in most countries. Evidence that would be useful to show this would be:

• A copy of the publication (or a reliable link to it)
• When the publication was made
• Who published it and where

Product sold or offered for sale

A product commercially sold or offered for sale in the US is likely to count as prior art in the US (but not in all other countries). Evidence that would be helpful to show this would be:

• Information about the product (e.g. manuals, review, brochure)
• Evidence that the product was offered for sale or sold in the US
• When the product was offered for sale or sold in the US

Links into the Internet Archive (Wayback Machine) at www.archive.org are a particularly effective means of showing past dates for both cases.

This site does not provide legal advice, please contact your lawyer if you need specific advice on prior art.