Anselm was born in Aosta at the foot of the Alps. After his mother's death he left home, wandered, and arrived in 1059 at the new Benedictine monastery of Bec in Normandy — drawn by the fame of its prior Lanfranc. Anselm took the habit at Bec and rapidly succeeded Lanfranc as prior (1063) and then abbot (1078).
It was at Bec that he composed the works that founded scholastic theology: the Monologion (1076), the Proslogion (1077–78), and a series of treatises that defined the method of using reason to deepen the understanding of faith — fides quaerens intellectum, 'faith seeking understanding.' The Proslogion contains the famous 'ontological argument' for the existence of God: a being than which nothing greater can be conceived must, by definition, exist.
Made Archbishop of Canterbury in 1093, he twice went into exile (1097, 1103) over the lay investiture controversy with the English kings William II and Henry I. His great theological work Cur Deus Homo ('Why God Became Man,' 1098) developed the satisfaction theory of the Atonement that has shaped Western theology ever since. He died at Canterbury on April 21, 1109. Pope Clement XI declared him a Doctor of the Church in 1720.