In contrast to the United States, most countries require that there have been no public disclosure of the invention anywhere in the world before the effective filing date of the patent application. This is often called an “absolute” or “universal” novelty requirement. However, this does not necessarily mean that the invention must be kept secret until all patent filings are completed. The U.S. is a member of an international treaty known as the Paris Convention that allows U.S. patent applicants to claim priority of their U.S. filing date in subsequent patent applications they file in member countries of the Paris Convention within one year (six months for design patents) after filing the U.S. patent application. The effective filing date in other Convention countries will be the U.S. filing date, and thus, so long as the invention was not public before the U.S. filing date, it will still meet the absolute novelty requirement in any country where International Convention priority can be claimed. The countries (177 as of 2021) that recognize a claim of priority can be found here. Obviously, not every country recognizes a claim of priority, among those not participating are Burma, Cape Verde, East Timor, Eritrea, Ethiopia, Fiji, Kiribati,Maldives, Marshall Islands, Micronesia, Nauru, Palau, Taiwan, Tuvalu, Vanuatu, and Yemen, although the United States has a bilateral treaty with Taiwan that permits claims of priority
In most countries it is possible to file a patent application so long as the invention has not been made public, regardless of whether patent applications have been filed in other countries. Where an invention has been made public before any patent application is filed, there are a handful of countries where patent protection may still be obtained, the most significant of which are the United States and Canada. If the invention is not made public until after a patent application is filed in an International Convention country, such as the United States, then the ability to file in other International Convention countries is preserved for one year from the original filing date, regardless of whether the invention is subsequently made public. Finally, there are a handful of countries where it is possible to obtain a patent even after the invention has been patented in another country. Indeed, for some countries the invention must be patented in some other country before a patent can issue. For example, to obtain a patent for certain British territories, such as the Channel Islands or Singapore, the applicant must already have obtained a U.K. patent. Similarly, to obtain a patent in Macao, the applicant must already have obtained a Portuguese patent.
Another important difference between U.S. patent laws and the patent laws of most other countries is that most other countries award the patent to the first person who files a patent application on the invention, while the U.S. awards the patent to the person who can prove that he or she made the invention first. This “first-to-file” system obviously gives incentive to promptly file patent applications outside of the U.S. (or obtain the earliest possible priority date by filing promptly in the U.S.). Of course, once the U.S. application is filed, the filing date is locked in in other Paris Convention countries so long as the requirements of the Paris Convention are met.