Theological reflection on friendship, as a particular form of Christian love, emerges in Holy Scripture and continues to be elaborated in the Christian tradition. However, "love of friendship" was at times absorbed into the other traditional understanding of love—"love of God and of neighbor." After a philosophical-historical study of the Greco-Roman roots of friendship in moral reflection, and how (and to what extent) this was appropriated in the Christian tradition, this book illustrates the transcendental character and the novelty of the Christian understanding of friendship found in Holy Scripture, focusing particularly on the most relevant texts in the Fourth Gospel where "love" and "friendship" stand to be important themes. It also shows how Saint Thomas Aquinas, through his exegesis of the Fourth Gospel, his synthesis of the Christian tradition, and his ability to rearticulate Christian theology through Aristotelian philosophy, inimitably defines the theological virtue of caritas as "friendship with God." In so doing he depicts friendship as the finality, the telos, of the Christian life. Finally, the book aims to show how the retrieval of a proper theology of friendship, rooted in Holy Scripture and Christian tradition, can enrich the life of an authentic Christian and contribute to the ongoing process of renewing moral theology.