Can a researcher use an article in their dissertation if it has already been published in a journal?

Whether a researcher may include a previously published article in a doctoral dissertation depends primarily on the publishing agreement concluded with the journal. If the research on which the article is based was at least 50% publicly funded, Articles 40 and 41 of the Scientific Research and Innovation Act apply. In such cases, the researcher may transfer rights to the publisher on a non-exclusive basis, meaning the author generally retains the right to reuse the article for purposes such as inclusion in a dissertation.

Regardless of the publishing contract, the researcher may always cite their own already published article in the doctoral dissertation.