At a time when Christian faith in the Trinity is both challenged by militant atheism and called to engage in serious dialogue with Islam, this book presents the biblical, historical, and experiential roots of Trinitarian faith. It shows how Christianity stands or falls with this faith in the Trinity, and why such as faith radically shapes personal life and public worship. It takes up major Trinitarian issues of today: such as naming the Trinity, the distinct personal existence of the Holy Spirit, and Trinitarian images. Highlights: - Displays the biblical roots of Trinitarian faith - Clarifies the development of official teaching about the Trinity - Confronts such major issues as naming the Trinity and the personal existence of the Holy Spirit - Accessible, constantly interesting, and stylishly written