Berthold III (c. 1110/1122 – 14 December 1188), a member of the Bavarian House of Andechs, was Margrave of Istria (as Berthold I) from 1173 until his death.
He was the son of Count Berthold II of Andechs (died 1151), ruler over Dießen in Bavaria, Plassenburg in Franconia and Stein in Carniola, and his first wife Sophia (d. 1132), a daughter of Margrave Poppo II of Istria. His brother Otto became Prince-Bishop of Brixen in 1165. A loyal supporter of the Hohenstaufen emperor Frederick Barbarossa, Count Berthold rose to one of the most important nobles, holding extended estates in Bavaria as well as in Franconia and in Carniola south of the Eastern Alps.
In 1173, he was appointed Margrave of Istria, succeeding Engelbert III, the last Margrave from the House of Sponheim and cousin of his mother Sophia. When in 1180 Emperor Frederick deposed the Welf duke Henry the Lion, he vested Berthold's son, Count Berthold IV, with the title of a Duke of Merania, thereby elevating the House of Andechs to princely status.