This brief note is not legal advice and is for educational purposes only.
This area can get complicated and you really should contact your attorney.
Foreign filing is filing for a patent application in a country/region other than where you originally filed. For example, if you filed in the US then once you get foreign filing permission from the USPTO (US Patent and Trademark Office) then you can file in other countries/regions (assuming they’re not on a banned list). The most common approach to foreign filing is via a PCT (Patent Cooperation Treaty) application which is an agreement between countries that allows for the reservation of patent filing rights. Put very simply it acts like an umbrella in reserving rights for an inventor to file in a foreign country or region at a later date. Not all countries are in the PCT although most of interest are (Taiwan is not). (See our other Brief Notes on this.) Check here to see “member states” or “contracting states” of the PCT and the 2 letter country/region abbreviation:
Foreign filing permission
Just like the US, many countries require you to get foreign filing permission if you invented in a country. The stated interest is to protect other countries from benefiting from an advanced technology that might be very critical or sensitive (think unbreakable encoding, hand sized hydrogen bomb, etc.) China requires this as well, even if you are a US citizen, if the invention was developed in China, you need a “confidentiality examination”.
Typical US usage
If you filed in the US, then using the PCT you can enter other countries/regions. For example, Europe, China, etc. See link above for member states. If the country/region you want to file in is NOT on the contracting states list tell your attorney promptly.
It gets complicated very fast
It gets complicated very fast if you have inventors from different countries and/or in different countries. Some countries require you to file in that country first and obtain permission for foreign filing, which you can imagine is impossible in some cases and becomes a Catch-22. For a peek at the complications see:
Foreign filing is possible, however it can get really complicated if you have multiple inventors from different countries and/or in different countries. Discuss with your attorney BEFORE filing. Caute procedere