This study offers an ecumenical exploration of human transformation through the examination of this topic in the thought of Karl Barth (1888-1968), a Swiss Reformed theologian; Joseph Ratzinger (b. 1927), a Roman Catholic theologian; and John Zizioulas (b. 1931), a Greek Orthodox theologian. Describing and understanding human transformation stands as a crucial task for theology because no one is simply born a Christian—in order to be a Christian one must become a Christian. The first chapter introduces this topic, the three theologians (highlighting their commonalities), and the three questions that guide the analysis of each theologian and the thesis as a whole: What is the goal of human transformation? What is the basis of human transformation? How are humans transformed? Chapters 2, 3, and 4 treat the topic of human transformation in the theology of Barth, Ratzinger, and Zizioulas, respectively. All three understand the goal of human transformation to be the prayer of the children of God, and locate its basis in God’s reconciling act in Jesus Christ—an act itself based in the primordial divine decision to be God pro nobis. Even within this broad agreement, however, differences are evident, especially with regard to eschatology. Consideration of how this transformation occurs reveals significant differences concerning the agency of Jesus Christ in relation to the Holy Spirit and the church. The final chapter explores 1) the convergences and divergences between Barth, Ratzinger, and Zizioulas regarding human transformation; 2) the contributions of this study to the interpretation of Barth, Ratzinger, and Zizioulas; and 3) the relationship between human transformation and participation in God. Throughout, attention is given to the relationship between Jesus Christ, the Holy Spirit, the church, the eschaton, and the triunity of God and human transformation. All three accounts of human transformation point beyond the transition between sinful and redeemed humanity to a dynamic anthropology in which the constant asking, receiving, thanking, and asking again is the very “ontological location” of the eschatological life of humanity: our being is in becoming.