Filing a US provisional application, publishing the invention in the priority interval and then obtaining a filing date at the EPO, claiming the priority date of the provisional seems to be a sensible way of seeking protection for your invention in Europe. Researchers in particular would like to publish their results as soon as they can and the publication in the priority interval should not be detrimental since the EP application will benefit from the priority date of the US provisional application.   However, it might in fact turn out that the claims of the EP application cannot validly claim the priority date of the US provisional application. This is due to the EPO’s very strict approach on added subject-matter. In order to decide whether the priority is valid, the EPO will look at the contents of the US provisional application. If the EP claims are not directly and unambiguously derivable therefrom, the priority is invalid. This in turn means that the publication of the invention in the priority interval will anticipate the EP claims. Accordingly, no or little European patent protection will be possible for the invention.   The risk of such an outcome is particularly high for US provisional applications that lack any claims and whose contents is rather limited, e.g. to a concrete description of a preferred embodiment of the invention. Most often, the EP claims will be a generalization of the specific teaching in the US provisional application. The EPO is very critical towards such generalizations and thus might be inclined to reject the priority claim.   Applicants can minimize this risk with a first filing in the US having a full disclosure and an adequate set of claims. This is only a rough overview. For further details and legal advice, please contact Fabian Lieb. 