This paper is concerned with the theoretical significance of Augustine in the historical development of the concept of ousia. There are references to the translation of ousia by essentia found throughout Augustine’s corpus; Augustine describes essentia as a ‘new word’ [novo quidem nomine]; and he is explicit about his preference for essentia instead of substantia as a translation for ousia. Augustine’s defense of the word essentia is ultimately related to the development of his understanding of the Trinity; but the background for Augustine’s preference for essentia is also related to the Manichaean controversy, as well as to the Neo-Platonic and Plotinian horizons, specifically on the problem of evil as it relates to the existence of God. This paper proposes the following objectives: 1) to discuss the historical and theoretical background to the translation of the Greek oὐσία into the Latin substantia or essentia, respectively; 2) an examination of the reasons Augustine gives for his preference for the translation of ousia by essentia; 3) the role that essentia plays in Augustine’s understanding of the Trinity, most specifically on the relation between ousia and hypostasis; 4) and finally, an appraisal of the Augustinian position vis-a-vis contemporary issues in philosophical and theological discussions. The thesis of this paper is that the priority of essentia enables Augustine to avoid the Arian position on the substantial difference of the persons of the Trinity, as well as the Sabellian position which collapses the difference of the persons back into a unity, and that, in the end, the essentia takes on for Augustine the characteristics of a divine name.