Yolanda of Flanders (Yolande de Hainault) ruled the Latin Empire in Constantinople for her son Philip of Namur from 1217 to 1219 after her husband Peter II of Courtenay was captured and imprisoned before he could reach Constantinople.
Yolanda was the daughter of Baldwin V, Count of Hainault, and Countess Margaret I of Flanders. Two of her brothers, Baldwin I and then Henry, were emperors in Constantinople. After the death of the latter in 1216 there was a brief period without an emperor, before Peter was elected. Peter sent Yolanda to Constantinople while he fought the Despotate of Epirus, during which he was captured. Because his fate was unknown (although he was probably killed), Yolanda ruled as regent. She allied with the Bulgarians against the various Byzantine successor states, and was able to make peace with Theodore I Lascaris of the Empire of Nicaea, who married her daughter. However, she soon died, in 1219.