Theology in the early fourth century was engrossed with questions about the nature of the Son of God in relation to the Father. How was he 'from the essence' of the Father? Was there a time when he was not? While generally treated as a minor footnote in the development of trinitarian and christological theology by most modern scholars, Eusebius of Caesarea provides a rich and original contribution to these debates about the trinity and theology in the midst of the Arian controversy. This project explores the theological framework of Eusebius, focusing specifically on his understanding of the Son of God. Therein, it proposes and employs an underutilized lens to view the bishop - according to his exegetical strategies and his explicitly theological works. In doing so, Eusebius' primary understanding of the nature and role of the second person of the Trinity comes to the the Son is truly Son. By focusing on his theology of the Son in multiple facets - trinitarianism, cosmology, soteriology, and Christology - his unique theological contribution to the church becomes clear. Eusebius is an important transmitter of Origenian theology and a foundational thinker for the later fourth and early fifth century.