The aim of this paper is to present the Eriugenian concept of the First Cause as developed in Book Two of his Periphyseon. The paper begins with Eriugena’s fourfold division of nature, and focuses upon his concept of the second form of nature, which consists of primordial causes. Eriugena’s view that God the Father has established in the Beginning, i.e. in His Son, the primordial causes of everything that are at once eternal and created, has led to many misconceptions and accusations of pantheism and subordinationism. These problems can be resolved against the background of Eriugena’s interpretations of Divine creative activity as well as his Trinitarian considerations.