U.N.O.S., the United Network for Organ Sharing, was set up by the federal government to oversee all organ donation and transplantation in the United States.U.N.O.S. regulates and certifies all transplant centers across the nation and establishes guidelines for donation, procurement, and transplantation of all human organs and tissues. U.N.O.S. also works with and certifies the regional O.P.O.'s or organ procurement organizations which recover donated organs and tissues and then places them with recipients based on the national U.N.O.S. registry.

NOTE: UNOS policies allow patients to be listed with more than one transplant center (multiple listing), and thus the number of registrations may be greater than the actual number of patients.