Persistent identifiers (PIDs) are permanent references to a digital object (document, file, website ...) or person. PIDs make it easier to link and retrieve publications and research results and to link authors with their works. PIDs must be unambiguous and refer to the correct version of the publication or research data long-term. PIDs for digital objects (e.g. DOIs and handles) and for people (e.g. ORCID iDs) even allow direct access to the digital objects or to information about the person via a resolver service.