William of Montferrat (early 1140s – 1177), also called William Longsword (modern Italian Guglielmo Lungaspada; original Occitan Guilhem Longa-Espia), is the Count of Jaffa and Ascalon, the eldest son of William V, Marquess of Montferrat and Judith of Babenberg.
He is the older brother of Conrad, Boniface, Azalaïs, and Renier, and a cousin of both Frederick I, Holy Roman Emperor and Louis VII of France.