Joscelin of Louvain, also spelled Jocelin de Louvain and Jocelyn of Leuven, (1121–1180) was a nobleman from the Duchy of Brabant who settled in England having married an English heiress. Through his youngest son, the House of Percy — as the Earls and later the Dukes of Northumberland—became the most powerful family in Northern England. He was brother-in-law to King Henry I, whose second wife was Joscelin's sister Adeliza of Louvain.