[After reviewing various proposals concerning the structure of Augustine’s De Trinitate, the author presents a structural analysis of that work using the notion of “realms of meaning” found in Bernard Lonergan’s Method in Theology. It suggests that Augustine’s treatise comprises four distinct sections which present an account of the Trinity from the perspective of a biblically informed common sense (Books 1–4); of theory (Books 5–7); of interiority (Books 8–11); and finally of transcendence (Books 12–15).]