Queen Judith or Iudit (died 19 April 843) was the second wife of Louis the Pious, Holy Roman Emperor and King of the Franks.

Judith was the daughter of Count Welf and a Saxon noblewoman named Eigilwi. She married King Louis in Aachen in 819, and the couple had a daughter, Gisela, and a son, Charles the Bald. Judith ensured that Charles received a share of the kingdom, just like his three half-brothers from Louis' first marriage. This contributed to the ensuing civil war among Louis and his sons. Rebels temporarily imprisoned Judith in the Convent of Poitiers on allegations of adultery during 830. From 833 to 834, she was exiled in Tortona. Judith was buried in St. Martin in Tours.

Judith was the first member of the Elder House of Welf to have a leading role in the Frankish Kingdom. Whether by coincidence or through Judith's influence, in the years following her marriage to Louis her mother and both of her brothers gained important offices in the kingdom. Her sister Hemma married Louis the German, a son of Louis the Pious' from his first marriage, in 827.