What is a priority filing?

A patent application filed in one country only provides protection for that country, therefore, multiple foreign filings are necessary to have wide geographical coverage. The system of priority filing was set up by the Paris Convention which was signed by almost all countries. This convention determines that a first patent application filed in one country party to the convention will determine the “priority date” of the invention for any applications filed within 12 months on the same invention in any country. The priority date is considered the date on which the invention was deposited such that any documents which are made public after that date can not considered by the patent offices for determining the patentability of the invention. 

The use of the system of the priority filing allows applicants to postpone costs relating to filing in different countries of interest for 12 months. In the meantime information on the commercial relevance of the invention can be obtained.