Persistent identifiers (PIDs) are provided by different organizations, so called PID providers. While often one provider focuses on one type of PID, a provider could have a service range offering several different types of PIDs. Vice versa, one type of PID can be offered by more than one provider, such as in the case of DOIs, but could also be exclusive to one particular provider, such as in the case of ORCID. The following table gives an overview of PIDs and PID providers.