Siegfried III of Eppstein (c. 1194 - 9 March 1249) was the Archbishop of Mainz from 1230 until 1249. Siegfried was a nephew of Siegfried II of Eppstein, Archbishop of Mainz, and also Theodoric II of Wied, Archbishop of Trier, through his mother's side. In 1220 he became a member of the cathedral in Mainz, provost of St Bartholomew in Frankfurt, and provost of St Peter and Alexander in Aschaffenburg. In October of November he was elected the archbishop of Mainz in succession to his uncle. As Archbishop Siegfried was a skilled politian and a supporter of the Hohenstaufens, but he was also like all other Imperial princes through the Confoederatio cum principibus ecclesiasticis of 1220 and he expanded the size of the secular territory.