Eustace Garnier (also Grenier, Granarius, Grenarius) (died June 15, 1123) was an important crusader lord, and Constable of the Kingdom of Jerusalem. He was from Beaurain-Château, in Thérouanne in northern France (at the time in the County of Flanders); he has accompanied Hugues II of St. Pol on the First Crusade, in the retinue of Godfrey of Bouillon.