Applying for international patents: Most countries maintain their own separate patent and trademark offices, and typically (Europe being a partial exception), patents operate within national borders. Thus a US patent, for example, covers just the US.
The Paris Convention: The process of extending a patent application to cover multiple countries was worked out by several international treaties. One important treaty, which is still in effect, was the 1880’s era Paris Convention. This established that, for example, a foreign patent office will recognize the priority of a US utility patent application (or provisional patent application) for up to 12 months after its initial filing date.
This was a good start, but it often takes more than 12 months to determine if a new invention is commercially important. It is very expensive to file patent applications in many different countries. So for many applicants, 12 months just wasn’t long enough.
The Patent Cooperation Treaty: To extend this time, in the 1970’s the Patent Cooperation Treaty (PCT) was enacted. This treaty is a bit complicated. Think of it as a temporary “holding tank” for patent applications. The key idea is that if you file a PCT application within 12 months of the filing date of the original patent application, you can extend your ability to then file international patents to 30 months from the filing date of the original patent application. Note that the PCT treats both utility patent applications and provisional patent applications in the same way.
After 30 months from the filing date of the original patent application, however, you then need to make some tough decisions. It typically costs thousands of dollars to file (i.e. enter the national phase) in each separate country. So unless the invention is really very promising, often applicants either continue on only in the US, or else only file nationally in a few select countries.
The Patent Prosecution Highway: Typically, each local (national) patent office will then want to examine the patent application itself. This is both expensive and duplicative of resources. To help streamline the process, in the late 2000’s, various Patent Prosecution Highway (PPH) agreements were initiated, typically on a bilateral (country-to country) basis. Here, if a patent application has claims allowed by one (PPH) country’s patent office, the applicant can petition to have these claims accepted by other participating PPH offices. The US participates in the PPH, as do a number of other countries. The PPH is great when it works, but it is presently a patchwork of agreements rather than a comprehensive international treaty. So view the PPH as being somewhat in the “pilot” or “beta” stage.