Gisa (also spelt Giso) was Bishop of Wells from 1060 to 1088.
Gisa was born in Lorraine, possibly from the village of St Trond in modern Belgium, and was among a number of foreign churchmen brought to England by Edward the Confessor. At first he held the position of king's chaplain, but in January of 1060 or possibly January of 1061 he was elected to become Bishop of Wells. Pope Nicholas II consecrated him on 15 April 1061 in Rome. He went to Rome for consecration because the current archbishop of Canterbury was Stigand, who successive popes had excommunicated for various irregularities, and traveled in company with another bishop Walter of Lorraine Bishop of Hereford and Tostig Godwinson. The Vita Edwardi says that he was "most suitably and excellently trained."
On his arrival in the see he found the church there quite poor. He constructed cloisters to the north of Wells Cathedral and communal buildings to the south for the canons. He ordered the canons to live together under a rule, but exactly which rule it was is unknown. After the Conquest, he introduced the veneration of new saints into his cathedral, as well as setting up an archdeacon in the diocese for the first time He also wrote a history of the church. He worked to restore lands formerly held by the bishop or cathedral that had been unjustly acquired by others.
Gisa obtained land grants for the upkeep of the church and canons from Edward and later Harold Godwinson and William I of England. He is mentioned many times in the Domesday Book as the holder of land for the see, and was notorious for acquiring land throughout his bishopric. The only surviving writ of Harold's issued while Harold was king dealt with Giso's rights as bishop, and was addressed to Abbot Aethelnoth of Glastonbury, the sheriff of Somerset, and the thegns of Somerset.
After the Norman conquest of England, Giso supported William. He helped consecrate Lanfranc as archbishop of Canterbury in 1070, and attended the Council of Windsor in 1072 and the Council of London in 1075. At a later church council, Giso asserted his authority over the abbots of Muchelney and Athelney, but failed to do the same to Thurstan, Abbot of Glastonbury.
In 1080, Adelard of Bath was born to Fastrad, a member of Gisa's household.
He died in 1088 and was buried at Wells Cathedral. When he died, he, along with Saint Wulfstan of Worcester, were the only remaining bishops still remaining from Edward the Confessor's appointments. His tomb was opened in 1979, and a cross with verses from the Mass for the Dead inscribed on it was found in his tomb.