The mystery of the Trinity is the central Christian belief that defines God's essence, God's ongoing love for humanity, and saving grace. Yet, over the past few centuries, especially in the West, Christians have either ceased believing in the Trinity or simply no longer recognize its relevance in their ecclesial or individual lives. Written in an ecumenical spirit that engages contemporary questions and theological viewpoints, articulates the mystery of the Trinity for people formed by modern historical consciousness, science, awareness of the equal dignity of men and women, and respect for world religions.By first identifying contemporary problems with the Christian proclamation of the Trinity in our culture and major differences among modern theologians, John Farrelly, OSB, explores Scripture, the life and message of Jesus Christ, the various stages of the development of Trinitarian doctrine in Christian History, the relation of the Trinity to creation and salvation, the generation of the Son from the Father within the Trinity and the procession of the Holy Spirit from Father and Son, and the meaning of three persons in one God. He concludes by reflecting on the implications this renewed theology of the Trinity has for ecclesiology and Christian spirituality in our twenty-first century world, especially in relation to other world religions.