The PCT (Patent Cooperation Treaty) is a treaty framework that lets you file a single international patent application instead of filing separately in each country from the start. That application has effect in every PCT Contracting State from the filing date. But the PCT does not grant an "international patent" — there is no such thing as a single patent that protects you worldwide. The decision to grant a patent still belongs to each destination country's or region's own patent office, in a stage called the National Phase.
The PCT is an international filing framework
The PCT is an international treaty with more than 150 Contracting States. It lets applicants seek patent protection in multiple countries at once by filing a single international application, in one language, with one initial set of fees — instead of filing a separate application in each country from day one.
One international application, not one international patent
This is the most common misconception about the PCT: the PCT gives you a single "international patent application," not a single "international patent." Whether a patent is actually granted still rests entirely with each destination country's or region's own patent office, in a stage called the National Phase (see Entering the National Phase). Each office examines and decides independently under its own law, and a decision in one country does not bind any other office.
The international phase
After you file a PCT application, it enters what's called the international phase, which includes several parts:
- International search: an International Searching Authority (ISA) searches for relevant prior art and produces a search report together with a preliminary, non-binding written opinion on patentability.
- International publication: the application is published, generally around 18 months after the priority date.
- International preliminary examination: an optional further step (Chapter II) an applicant can request for a deeper, non-binding opinion, with an opportunity to amend the application. This opinion also does not bind any destination office.
None of this is patent examination in the sense of a grant decision — it's information and a preliminary opinion to help you assess your position before deciding which countries to actually pursue in the National Phase.
Every Contracting State is automatically "designated"
A PCT application automatically has effect — is "designated" — in every PCT Contracting State from the filing date. You don't need to choose your target countries when you file; you choose later, when deciding which countries to enter the National Phase in. That's the PCT's main advantage: it lets you defer the decision and cost of choosing your target countries for a period of time.
Paris Convention priority and the PCT are not the same thing
Paris Convention priority is a different mechanism from the PCT. If you file a first application in one country (say, Thailand), you have 12 months from that first filing date to file an international application under the PCT claiming priority from that first application. A PCT application filed within that window is treated as if it had been filed on the same date as the first application, and is shielded from intervening events during that period — such as publication of the invention or a filing by someone else. In short: Paris Convention priority is a filing-date mechanism; the PCT is an international filing framework. The two work together, but they are not the same thing.
PCT vs. direct filing: how to decide
Key factors to weigh:
- Number of target countries: if you want protection in several countries, or aren't yet sure which ones, the PCT lets you defer that decision. If you already know you only need one or two specific countries, direct filing may be more straightforward.
- Timing: the PCT buys extra time before you have to commit significant spend in each destination country — useful if you still need time to assess the market or secure funding.
- Information from the international search: the ISA's search report and preliminary opinion help you assess your chances before committing to National Phase entry in multiple countries.
There's no single right answer for every case — weigh it alongside your other business factors. For a full decision framework, see International Filing Strategy.
