For nearly one thousand years, theologians, philosophers, and Christian apologists have felt the effects of Anselm of Canterbury. Anselm’s theological method was rigorous, and represented a seismic shift in medieval thought. He is widely considered the founder scholastic theology, and he has been called the church’s “second Augustine.” His treatise on the atonement, Cur Deus Homo was the first to systematically articulate the penal substitution theory of the atonement, which was later developed by John Calvin and widely embraced by Reformed and evangelical churches. He was also the first to construct and systematize the ontological argument for the existence of God. The Major Works of Anselm of Canterbury contains Anselm’s important theological and philosophical writings: the Proslogium, the Monologium, and Cur Deus Homo, plus his exchange with Guanilon.