Wisconsin state law forbids the practice of medicine without a license from the Examining Board (Board) (defendant). State law also defines and forbids various acts of professional misconduct. The Board, which is composed of practicing physicians, has the authority to warn and reprimand, as well as to suspend or revoke a license. The Board initiated an investigative proceeding against Dr. Larkin (plaintiff), a doctor, to determine whether he had engaged in certain proscribed acts. After going forward with its investigation, the Board sent Larkin a notice that a contested hearing would be held to determine whether he had engaged in the proscribed acts and that the Board would determine whether to suspend his license based on what it learned in the hearing. Larkin sought a restraining order against the hearing. The district court granted Larkin’s request and later granted a preliminary injunction upon determining that the combination of the Board’s prosecutorial and judicial functions violated constitutional guarantees of due process. The United States Supreme Court granted review of the case.