Guy (born c. 1225—died March 7, 1305, Compiègne, Fr.) was the count of Flanders (from 1278) and margrave of Namur (Namen). He was the son of Margaret, countess of Flanders and Hainaut.

The government of Guy of Dampierre was unfortunate. It was in the interest of the Flemish weavers to be on good terms with England, the wool-producing country, and Guy entered into an alliance with the English king Edward I against France. This led to the invasion and conquest of Flanders by the French king Philip IV the Fair in 1300. Guy with his sons and the leading Flemish nobles were taken as prisoners to Paris, and Flanders was ruled as a French dependency. The Flemish rose in rebellion, however; a French garrison at Bruges was massacred on May 19, 1302, and on the following July 11 a French army of invasion was defeated near Courtrai. The aged Guy died in captivity before the French recognized the independence of Flanders in the Treaty of Athis-sur-Orge (1305).