William III of Geneva

William III of Geneva (1280–1320) was count of Geneva from 1308, when he succeeded his father Amadeus II. A 1291 treaty with Savoy first betrothed him to Beatrice of Savoy, and after its annulment he married her sister Agnes, daughter of Count Amadeus V, in 1297.

His succession brought a dispute with his mother Agnes of Chalon, settled by agreement in 1308. That October he made perpetual peace with Savoy, acknowledging several castles as its fiefs, and in 1316 he did homage to the dauphin of Viennois.

His children with Agnes included Amadeus III, born in 1311, who succeeded him. He made his will at Annecy in April 1319 and died the following year.