Joscelin III of Edessa (1159 – after 1190) was the titular Count of Edessa. He was the son of Joscelin II and his wife Beatrice. He inherited the title of Count of Edessa from his father, Joscelin II, although Edessa had been captured in 1144 and its remnants (including the Lordship of Turbessel) conquered or sold years before he took the title.
Joscelin lived in the Kingdom of Jerusalem and managed to gather enough land around Acre to set up the Seigneurie of Joscelin. His sister, Agnes of Courtenay, had been the first wife of King Amalric I before he succeeded to the throne, and was the mother of Baldwin IV and Sibylla. In 1164 Joscelin was taken captive by Nur ad-Din Zengi at the Battle of Harim. He remained a prisoner until 1176 when Agnes paid his ransom of 50,000 dinars, probably with support from the royal treasury. His nephew Baldwin then made him seneschal of Jerusalem. He faced some rivalry from the king's paternal kindred, led by Raymond III, Count of Tripoli.
In 1180 Joscelin went as an ambassador to the Byzantine Empire. After the betrothal of Princess Isabella I of Jerusalem (Baldwin's half-sister) to Humphrey IV of Toron that year, the Toron estates passed to the crown in exchange for a money fief. Baldwin IV granted part of them, Chastel Neuf, to Joscelin, and awarded Agnes an income from the usufruct, or produce, of Toron. Agnes died in late 1184, a few months before her son.