The issue of how to correctly claim priority for a European patent application is one which has come up again and again over the years. Now, a referral has been made (jointly as G 1/22 and G 2/22) to the EPO’s Enlarged Board of Appeal (EBA), asking questions on how priority claims should be handled for PCT applications where there are different applicants for different countries. 

This briefing will provide some background about the referral, and a reminder on how to best ensure that claims to priority in patent applications are safely made. Our advice is unchanged: careful checks should be made before filing a priority-claiming patent application, to ensure that the applicant(s) claiming priority are entitled to do so.  


The fact that questions around patent priority have come up with relative frequency over the years is perhaps unsurprising. The priority mechanism is a powerful one, enabling applicants to take advantage of the date of filing a first patent application covering the invention, after which details of the invention can be disclosed to the public. Within 12 months, the final patent application can be filed with more information and data about the invention, but the effective date of filing is treated as the first application filing date when novelty and inventive step are considered. The right to claim priority is one which goes all the way back to the Paris Convention of 1883. 

On the face of it, claiming priority correctly is straightforward enough. The Paris Convention indicates that the right to claim priority belongs to any person, or their successor in title, who has filed an earlier patent application for a patent for the same invention. However, over the years questions have arisen about the meaning of “the same invention” and the meaning of “any person”. The EPO also views priority claims strictly, and many applicants have unwittingly fallen foul of their stringent approach. Our summary of the best practice for correctly claiming priority can be found in our earlier article.  

Different applicants for different PCT states 

A further subtlety to patent priority issues has been raised in the questions recently referred to the EBA in G 1/22 and G 2/22.  

The Patent Cooperation Treaty (PCT) is a system which allows a single patent application to be filed covering multiple territories around the world. The applicant can elect to file the application for all countries, or for a selection of them, and applicants can be different for different countries. This was especially common when US law required patent applications to be filed in the name of the inventors. This typically resulted in the US part of the PCT application having the inventors as applicants, with the applicant for the remaining territories being, for example, an organisation by which the inventors were employed. 

The facts in this case (patent EP1755674 and application 16160321.2) 

The facts underlying G 1/22 and G 2/22 arise from such a situation. G 1/22 relates to a granted patent and G 2/22 to a divisional application related to that patent; for simplicity we will refer to the patent only.  

When the original priority application was filed, it was filed in USA in the names of the inventors X, Y and Z. When the PCT claiming priority was filed, the applicants were X, Y and Z for USA only; for all other territories including Europe, the applicants were company A and university U. 

For the European patent, had the priority been validly claimed? That is, was the applicant for the European part of the PCT application the person “who had filed the priority application, or their successor in title”? The share of the priority right held by inventor X had been assigned to company A before the PCT was filed. The share of that right held by inventors Y and Z had incorrectly been assumed to have been transferred to university U, but in fact it had not. Therefore, when the PCT application was filed, the right to claim priority belonged to jointly to A, Y and Z. 

The question then is, does the fact that the PCT application was filed listing all of X, Y, Z, A and U as applicants, albeit for different territories, mean that the priority claim was validly made? This is described in the referring decision as the “PCT joint applicants” approach. This would mean that all the PCT applicants are considered to be applicants who are treated as joint applicants in proceedings before the EPO. The inclusion of the parties who hold the right to claim priority means that the priority claim was validly made. 

The referring Board of Appeal was not itself persuaded by this idea. They could not identify any provision which results in PCT applicants for one territory being regarded as being the applicants for other territories, unless the relevant boxes had been ticked on the PCT filing form. However, they pointed to earlier cases, including of national courts of EPC states, in which a joint filing of an application had been treated as being an implied agreement of the transfer of the right to claim priority. This was enough for the priority claim to have been validly made. 

The referral 

The Board considers that this issue is one of fundamental importance and so questions have been referred to the EBA. The EBA is first asked to confirm that the EPO has jurisdiction to determine whether priority has been validly claimed. Assuming the answer is yes, the main question is: 

Can a party B validly rely on the priority right claimed in a PCT-application for the purpose of claiming priority rights under Article 87(1) EPC in the case where 

1) a PCT-application designates party A as applicant for the US only and party B as applicant for other designated States, including regional European patent protection and 

2) the PCT-application claims priority from an earlier patent application that designates party A as the applicant and 

3) the priority claimed in the PCT-application is in compliance with Article 4 of the Paris Convention? 

If the EBA decides that the answer to this question is “no”, many patents and applications may be vulnerable to a loss of priority, when a priority application has been filed in the name(s) of the inventor(s) and no assignment of the right to claim priority is in place before the PCT application is filed. Although US applications no longer required to be filed in the names of the inventor(s), this change only took effect in 2012, so there are many patents and perhaps still some pending applications where this fact pattern may apply. 

Previous decision 

It is worth noting that the fact pattern appears to resemble that of the 2009 UK High Court Case Edwards Lifesciences AG v Cook Biotech Inc ([2009] EWHC 1304 (Pat)). In that case, the US priority application had been filed in the names of the three inventors. The PCT application was filed with Cook Biotech Inc as applicant for most territories, and the three inventors as the applicants for USA. In that case, the UK part of the European patent was found not to have a valid claim to priority, because the right to claim priority had only been transferred from one of the inventors to Cook by virtue of employment. The other two inventors were not employed by Cook and had not assigned their share of the right to claim priority to Cook, so Cook’s claim to priority was found not to be valid. The “PCT joint applicants” approach does not appear to have been contemplated by the judge. 

This decision is included in documents on the file in the G 1/22 referral, but was not discussed in the referring decision. 


This new EBA referral underlines the need to take care over priority, and the right to claim it. Priority is a very powerful right and should only be useable by correctly entitled parties.  

The possibility of falling foul of priority challenges can be avoided by ensuring that all paperwork is in order, before a PCT application is filed. In some cases, an inventor’s right to claim priority may automatically be transferred to the PCT applicant by employment, but this depends on the relevant law in the country of employment, and/or of specific provisions in any employment contract.  

The safest route is for an inventor to complete an explicit assignment of the right to claim priority before the PCT application is filed (of course, such an assignment should only transfer the right to claim priority for countries where it is desired that the assignee will be the future applicant). If an assignment can’t be completed in time, the priority-claiming application should be filed in the same name(s) as the first application. The later application can always be assigned in due course, after the priority claim has been correctly made. 

More detailed guidance on how to ensure that a priority claim is valid is set out in our earlier summary. If you have any questions on any aspect of patent priority, please contact any of our patents team or email us.

This article is for guidance only and should not be taken as legal advice.