Joanna of Penthièvre was a French noblewoman born in 1326. She was the daughter of Charles of Blois and Joanna of Penthièvre, and she became the heiress of the Duchy of Brittany. Joanna was known for her strong claim to the duchy during the Brittany War of Succession, which was a conflict over the control of Brittany in the 14th century. In 1341, after her father's death, Joanna's claim was contested by John of Montfort, leading to a protracted struggle for power. Despite her efforts to secure her position, she faced significant challenges and ultimately lost the duchy. Joanna's life reflects the complexities of noble lineage and territorial disputes in medieval France.