Catholics believe in one God in three persons: a Trinity of Father, Son, and Holy Spirit. This explores the theological development of the doctrine of the Trinity, from its source in revelation through its refinement by the first seven ecumenical councils and its ongoing theological articulation.

God for us : The Trinity and Christian life / Catherine Mowry LaCugna.
Trinity : nexus of the mysteries of Christian faith / Anne Hunt.
The trinitarian theology of Saint Thomas Aquinas
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The Christian doctrine of God: one being three persons
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Deus Trinitas: the doctrine of the triune God
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The Trinity
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An introduction to the Trinity / Declan Marmion and Rik Van Nieuwenhove.
The Trinity / Karl Rahner
The Trinity: Retrieving The Western Tradition
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The Christian Trinity in History
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What are they saying about the Trinity? / Anne Hunt.
Nicaea and its legacy: an approach to fourth-century Trinitarian theology
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Trinity and truth
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Trinity and creation / Boyd Taylor Coolman, Dale M. Coulter, eds.