Jeanne of Flanders (1199/1200 - 1244) was countess of Flanders and Hainaut.

She was the eldest daughter of Baldwin IX of Flanders, who was also (as Baldwin VI) count of Hainaut. Her mother was Marie of Champagne.

In 1202 Baldwin left on the Fourth Crusade, and Marie left to join him two years later, leaving Jeanne and her baby sister in the care of their uncle Philip of Namur.

Jeanne's mother died in 1205, and her father died the next year, leaving her a five-year-old orphan under the guardianship of Philip of Namur. He continued as regent as well, ruling in her name rather than her father's. Philip soon put his nieces in a difficult position. He became betrothed to a daughter of King Philip Augustus of France, and give the king custody of the two girls. Philip Augustus in turn agreed to sell their custody to Enguerrand de Coucy, who probably planned to marry Jeanne when she came of age. But these plans fell through, and in the end she married Ferrand of Portugal in Paris in January 1212. He was the nephew of Jeanne's great-aunt-by-marriage Matilda of Portugal.

While on their way to Flanders the newlyweds were captured by Jeanne's first cousin Louis (the future Louis VIII of France), eldest son of Philip Augustus and Jeanne's aunt Elizabeth of Flanders. Louis' aim was to acquire his dead mother's dowry, a large piece of Flemish territory including Artois, which Jeanne's father had taken back by force after Elizabeth's death.

Released after this concession, Jeanne and Ferrand soon joined the old allies of her father, king John of England and Emperor Otto IV, in an alliance against France. They were decisively defeated at Bouvines in July 1214, where Ferrand was taken prisoner.

Ferrand was to remain in French hands for the next 12 years, while Jeanne ruled alone. During this period Jeanne ended up at odds with her younger sister Margaret over the latter's inheritance, a matter complicated by questionable validity of both of Margaret's marriages. A war between the sisters broke out, which only added to difficulties caused by famine.

In 1225 a man appeared who claimed to be Jeanne's father Baldwin, returned after 20 years. He soon became the focus of a popular revolt, which Jeanne only put down with aid from Louis VIII.