Both the novelty and the non-obvious assessment are based on the body of knowledge (prior art) which was publicly available before the filing date of a patent application. Thus, publications after the filing date are not considered when assessing novelty and non-obviousness. Essentially all industrially relevant countries have signed the Paris Convention, which is the foundational international treaty that established the concept of patent priority. The TRIPS Agreement obligates its member countries to adhere to key provisions of the Paris Convention, including the right of priority, thus making it a widely accepted international standard.

The concept of priority enables the applicant to utilize the earlier filing date of a priority patent application P for a subsequent patent application S. As shown below, the applicant can file a priority patent application P at office A and a subsequent patent application S at office B. This has the following effect on the consideration of Prior Art publications A, B and C during the patent examination. Prior Art A was published before both patent applications P and S. Prior Art B was published between the filing of the patent applications P and S. Prior Art C was published after both patent applications P and S.

During the examination, the Prior Art A publication is considered of both patent applications P and S. Prior Art C is not considered for either application P and S, because it was published only after the filing of the patent applications. As usual, Prior Art B is not considered during the examination of the priority patent application P, because Prior Art B is published after the filing date of the priority patent application. However, during the examination of the subsequent patent application S the priority takes effect, and Prior Art B is also not considered during the examination of the subsequent application S.

Claiming the priority requires:

1. The subsequent application S to be filed within 12 months after the filing of the earlier priority application P. There is no way to extend the priority period beyond 12 months, also not by chaining multiple priority periods.
2. The priority and the subsequent applications must be assigned to the same applicant.
3. Both applications must be drawn to the same invention.

The priority can be used at patent offices across multiple countries. Thus, after filing a first patent application for an invention, the applicant has up to 12 months to decide, whether additional patent applications in other countries are intended.

Using Provisional Applications for Priority

When people talk about “filing something quickly to secure a date,” they’re usually talking about a first filing that anchors the priority date, and then a later filing that builds on it. In the United States, a common way to do this is to start with a provisional application. A provisional application is not examined and automatically expires after 12 months, but it can still be extremely useful because it can establish a priority date for a later, full (non-provisional) application.

The practical upside is that a provisional can be faster and cheaper to file, and it immediately gives you “patent pending” status. The practical downside is also simple: the provisional only helps for what it actually disclosed. If the later application includes important details that were not described in the provisional, those parts won’t benefit from the earlier date. In other words, the priority date is only as strong as the technical disclosure behind it.

If you plan to file internationally, it’s also worth knowing that “provisional” is a US concept. Other patent offices do not treat a US provisional as a local filing type, they simply treat it as your priority document (if you claim priority from it). In that context, formalities matter: some offices require a certified copy of the priority document, while others can retrieve it through the WIPO Digital Access Service (DAS).

Partial and Multiple Priorities

Real inventions rarely “snap” into existence all at once. More often, the core concept is filed first, and then the implementation gets refined. The priority system can handle this. Many jurisdictions allow multiple priorities, meaning a single later application can claim priority from more than one earlier application.

However, each claim only gets the earlier date if the earlier filing actually supports it. If an early filing describes the baseline approach, and a later filing adds an important optimization or variant, then the baseline claims may benefit from the earlier date, while the optimization claims may effectively have the later date. You’ll sometimes see this described as partial priority. Different parts of the later application can have different “effective” dates because they trace back to different disclosures.

Some countries also have a concept sometimes called internal (domestic) priority, where you file an improved application at the same patent office within the allowed period and still keep the earlier date for what was already disclosed. To make it simple: Priority is tied to disclosure, not to intent.

Secure Your Priority Date

In a first-to-file world, an early priority date is most important, but the right filing approach depends on how quickly your technology is evolving and how clear you are about where you ultimately want protection.

It’s also worth remembering that priority dates become part of the public record once applications publish. Competitors use them to reconstruct timelines, gauge how fast a space is moving, and sometimes to infer filing strategies. From the other side, tracking priority dates across a technology area can reveal patterns in R&D activity and where innovation pressure is building.

The takeaway is straightforward: secure your priority date early. Every novelty challenge and prior art dispute will be measured against it.