Nontrinitarianism is a form of Christianity that rejects the mainstream Christian theology of the Trinity—the belief that God is three distinct hypostases or persons who are coeternal, coequal, and indivisibly united in one being, or essence. Certain religious groups that emerged during the Protestant Reformation have historically been known as antitrinitarian.

Christian theology is the theology – the systematic study of the divine and religion – of Christianity and Christian belief and practice. It concentrates primarily upon the texts of the Old Testament and of the New Testament, as well as on Christian tradition. Christian theologians use biblical exegesis, rational analysis and argument. Theologians may undertake the study of Christian theology for a variety of reasons, such as in order to:help them better understand Christian tenets make comparisons between Christianity and other traditions defend Christianity against objections and criticism facilitate reforms in the Christian church assist in the propagation of Christianity draw on the resources of the Christian tradition to address some present situation or perceived need education in Christian philosophy, especially in Neoplatonic philosophy