One of the key requirements to get a patent application is that the invention needs to be “new” or “novel”. That may sound a simple definition – the European Patent Convention states an invention is “considered to be new if it does not form part of the state of the art” (see link here). However, in practice, it is not so simple.
The “state of the art” is defined as “everything made available to the public by means of a written or oral description, by use, or in any other way, before the date of filing of the patent application.” There are no restrictions as to the geographical location, or the language or manner in which the relevant information was made available to the public. For example, the information could have been published in a book, presented as a lecture or published on a webpage.
Most commonly, written descriptions are used to challenge the novelty of the patent application, as the contents of the documents and their disclosure are the easiest to determine. The test is then – was the document actually available to members of the public before the date of filing of the patent application? In many cases, this is simple as the document may have a publication date. In other cases, it may be more challenging. For example, many scientific papers are published online months before they appear in official journals. The information in the papers may also have been made available as preprints on a server, such as arXiv.org. The relevant date for making the information available is then the date of uploading the scientific papers – and then only the information in the uploaded version. A later revised version of the paper will have a different (later) filing date.
In the European Patent Office (and most other European national patent offices), the prior art includes all information before the filing date of the patent application or – in the case in which priority to an earlier patent application is claimed – the priority date. Other countries, such as the USA, Japan, or Australia, consider that anything published by the inventors before filing the patent application does not need to be taken into account if the publication is less than twelve months before the patent filing date. More information on these so-called “grace periods” can be found here.