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Organizations that meet the contractual obligations of the DOI system and are willing to pay to become a member of the system can assign DOIs.[6] The DOI system is implemented through a federation of registration agencies coordinated by the International DOI Foundation,[7] which developed and controls the system. The DOI system has been developed and implemented in a range of publishing applications since 2000; by late April 2011 more than 50 million DOI names had been assigned by some 4,000 organizations.[8] By April 2013 this number had grown to 85 million DOI names assigned through 9,500 organizations. The DOI system uses, but is not formally part of, the Handle System.[9]
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