Baldwin II of Flanders (c. 865 -September 10, 918), nicknamed Calvus (the Bald) was the second count of Flanders. He was also hereditary abbot of St. Bertin from 892 till his death.

He was the son of Baldwin I of Flanders and Judith, a daughter of Charles the Bald.

The early years of Baldwin's rule were marked by a series of devastating Viking raids. Little north of the Somme was untouched. Baldwin recovered, building new fortresses and improving city walls, and taking over abandoned property, so that in the end he held far more territory, and held it more strongly, than had his father. He also took advantage of the conflicts between Charles the Simple and Odo, Count of Paris to take over the Ternois and the Boulonnias.

In 884 Baldwin married Aelfthryth (Ælfthryth, Elftrude, Elfrida), a daughter of King Alfred the Great of England. The marriage was motivated by the common Flemish-English opposition to the Vikings, and was the start of an alliance that was a mainstay of Flemish policy for centuries to come.

In 900, he tried to curb the power of Archbishop Fulk of Rheims by assassinating him, but he was excommunicated by Pope Benedict IV.

He died at Blandimberg and was succeeded by his eldest son Arnulf I of Flanders. His younger son Adalulf was the first count of Boulogne.