of the system can assign DOIs. The DOI system is implemented through a federation of registration agencies coordinated by the IDF. The cumulative number of DOIs has increased exponentially over time, from 50 million registrations in 2011 to 391 million in 2025. The rate of registering organizations ("members") has also increased over time from 4,000 in 2011 to 9,500 in 2013, but the federated nature of the system means it is not immediately clear how many members there are in total today. Fake registries have even appeared.

Nomenclature and syntax