Judith of Flanders, Countess of Northumbria, and later Duchess of Bavaria (1033 – 5 March 1094) was the wife firstly of Tostig Godwinson, Earl of Northumbria, and secondly of Welf I, Duke of Bavaria. Her niece was Matilda of Flanders, Queen consort of William the Conqueror, who was Judith's cousin.She was the owner of many books and illuminated manuscripts, which she bequeathed to Weingarten Abbey.