Gersende of Montlhéry was a notable figure in the medieval period, born around the late 10th century in Montlhéry, a region near Paris. She belonged to a noble family and was the daughter of Hugues de Montlhéry, a prominent lord. Gersende is often recognized for her marriages, which helped strengthen alliances among the French nobility. Her first marriage was to Hugues de Crécy, and later, she married Baldwin IV of Flanders. Through these unions, Gersende played a significant role in the political landscape of her time, influencing the relationships between various noble houses in France and Flanders.