Simon of Saint-Quentin (fl. 1245-48) was a Dominican friar and diplomat who accompanied Ascelin of Lombardia on an embassy which Pope Innocent IV sent to the Mongols in 1245. Simon’s account of the mission, in its original form, is lost; but a large section has been preserved in Vincent of Beauvais’ Speculum Historiale, where nineteen chapters are expressly said to be ex libello fratris Simonis.
The embassy of Ascelin and Simon proceeded to the camp of Baiju at Sitiens in Armenia, lying between the Aras River and Lake Sevan, fifty-nine days' journey from Acre.