The Patent Cooperation Treaty authorizes the filing of a single patent application to be treated as a patent application in countries around the world. This is most commonly referred to as a PCT. You can file an International patent Application pursuant to the rules of the PCT and the application will effectively act as a world-wide patent application, at least a patent application in these countries that have ratified the PCT. These countries are basically all of the countries where you would a patent.
The reason there is single world-wide patent but no world-wide patent is because patents are granted by individual countries but not by any international authority.
Individual countries have different patent laws which makes a uniform world-wide patent granting process impossible.
When one wants international patent rights it is best to draft the patent application so that it would be appropriate in the United States and China. The United States and China have the most stringent disclosure requirements.
Most inventors pursue filing their first patent application in the country in which they reside. This is referred to as direct filing. This option is accomplished pursuant to the regulations and laws of the country the application is being filed in. A U.S. patent application, such as a non-provisional patent application or provisional patent application is a direct filing option. From the United States perspective, a filing in a patent office other than the United States Patent and Trademark Office (USPTO) that is not filed pursuant to the Patent Cooperation Treaty (PCT) is considered a foreign application.
Note, if you file a patent application or a foreign patent application, you can still file an international patent application within twelve months of the earliest filing date and then your international patent application is given priority as of the filing date of the first application. This means that anything that happens after the earliest filing date cannot be considered prior art.
If you use an earlier filed patent application to support priority of the PCT Application, as is discussed above, or you file an international application without a previous direct filing, you need to enter into what is called “national phase” in every country where you wish to obtain a patent. You have 30 months from the priority filing date to enter the national phase in any country but it can get extremely expensive.
It is always best to seek advice from a patent attorney on where you should file your patent applications.