|A.K.A.||Marguerite d'Alsace, Margherita I di Fiandra|
|Death||November 15, 1194 (Bruges, Arrondissement of Bruges, West Flanders, Flemish Region)|
Margaret I of Flanders (circa 1145 - died 15 November 1194) was ruling countess of Flanders suo jure from 1191 to her death. She was the daughter of Thierry, Count of Flanders, and Sibylla of Anjou, and the heiress of her childless brother, Philip of Flanders.
In 1160 she married Ralph II, Count of Vermandois. Due to his leprosy, the marriage could not be consummated and remained childless. He died of leprosy in 1167 without issue.
In 1169 she married Baldwin V, Count of Hainaut, her third cousin once removed.
In 1191, her brother, the count of Flanders, died childless, and she as his heir claimed the county of Flanders with the support of her spouse. Her claims was questioned by the king of France who, with support of Ghent, declared Flanders escheated to the crown due to the lack of male heirs, a problem that was not solved until the Treaty of Arras by the mediation of the archbishop of Riems. They met some unrest among the nobility of the area, foremost by her brother's widow, who was given a large dower lands in the coastal and Southern Flanders where she provoked considerable unrest by high taxation.
The right of Margaret and her husband to the County of Flanders was not finally acknowledged until 1 March 1192. As was the custom at the time when women became rulers, her spouse was made her co-ruler.
As countess, she objected to all foreign legal independence in her lands, and accordingly, she prevented the Hanse merchants living in Bruges from acquiring a separate quarter and rights for themselves in the port of Damme.
Margaret died on 15 November 1194; as her husband had become count of Flanders only by marriage, he could not remain sole count, and Margaret was succeeded by their son.
- Isabella of Hainault, married Philip II of France
- Baldwin VI of Hainaut (1171–1205), also count of Flanders and Latin Emperor
- Yolanda of Flanders (1175–1219), married Peter of Courtenay, Latin Emperor
- Philip I, Marquis of Namur (1175–1212)
- Henry of Flanders (1176–1216), Latin Emperor
- Sybille (1179–9 January 1217), married c. 1197 Guichard IV, Sire de Beaujeu. They had a daughter, Agnes of Beaujeu.
- Eustace of Hainaut (d. 1219), regent of the Kingdom of Thessalonica
- Godfrey of Hainaut