Arnulf III (about 1055 - February 22 1071, in battle), was Count of Flanders and Count of Hainaut, as Arnulf I from 1071 to his death. He succeeded his father Baldwin VI in both counties. With his untimely death in battle in Saint-Omer, Flanders and Hainaut were separated again.

See also: Counts of Flanders family tree - Counts of Hainaut family tree - Other teenager rulers