Matilda of Flanders (French: Mathilde; Dutch: Machteld) (c. 1031 – 2 November 1083) was Queen of England and Duchess of Normandy by marriage to William the Conqueror, and regent of Normandy during his absences from the duchy. She was the mother of ten children who survived to adulthood, including two kings, William II and Henry I.

In 1031, Matilda was born into the House of Flanders, the second daughter of Count Baldwin V of Flanders and Adela of France. Flanders was of strategic importance to England and most of Europe as a "stepping stone between England and the Continent" necessary for strategic trade and for keeping the Scandinavian Intruders from England. In addition, her mother was the daughter of Robert II of France. For these reasons Matilda was of grander birth than William, who was illegitimate, and, according to some more romantic tellings of the story, she initially refused his proposal on this account. Her descent from the Anglo-Saxon royal House of Wessex was also to become a useful card. Like many royal marriages of the period, it breached the rules of consanguinity, then at their most restrictive (to seven generations or degrees of relatedness); Matilda and William were third-cousins once removed. She was about 20 when they married in 1051/2; William was some four years older, and had been Duke of Normandy since he was about eight (in 1035).

The marriage appears to have been successful, and William is not recorded to have had any bastards. Matilda was about 35, and had already borne most of her children, when William embarked on the Norman conquest of England, sailing in his flagship Mora, which Matilda had given him. She governed the Duchy of Normandy in his absence, joining him in England only after more than a year, and subsequently returning to Normandy, where she spent most of the remainder of her life, while William was mostly in his new kingdom. Matilda served as regent in Normandy during the absence of William six times: in 1066–1067, in 1067–1068, in 1069, in 1069–1072, in 1074 and, finally, in 1075–1076. She was about 52 when she died in Normandy in 1083.

Apart from governing Normandy and supporting her brother's interests in Flanders, Matilda took a close interest in the education of her children, who were unusually well educated for contemporary royalty. The boys were tutored by the Italian Lanfranc, who was made Archbishop of Canterbury in 1070, while the girls learned Latin in Sainte-Trinité Abbey in Caen, founded by William and Matilda as part of the papal dispensation allowing their marriage.