Binitarianism is a Christian theology of two personae, two individuals, or two aspects in one Godhead (or God). Classically, binitarianism is understood as strict monotheism — that is, that God is an absolutely single being; and yet with binitarianism there is a "twoness" in God. The other common forms of monotheism are "unitarianism", a belief in a single God with one aspect, and "trinitarianism", a belief in a single God with three aspects.

While binitarianism is sometimes used self-descriptively, it is also used to denote Christian error or heresy as are the following related terms:

Larry W. Hurtado of University of Edinburgh uses the word binitarian to describe the position of early Christian devotion to God, which ascribes to the Son (Jesus) an exaltedness that in Judaism would be reserved for God alone, while still affirming as in Judaism that God is one, and is alone to be worshiped. He writes:

…there are a fairly consistent linkage and subordination of Jesus to God 'the Father' in these circles, evident even in the Christian texts from the latter decades of the first century that are commonly regarded as a very 'high' Christology, such as the Gospel of John and Revelation. This is why I referred to this Jesus-devotion as a "binitarian" form of monotheism: there are two distinguishable figures (God and Jesus), but they are posited in a relation to each other that seems intended to avoid the ditheism of two gods" (Lord Jesus Christ: Devotion to Jesus in Earliest Christianity, William B. Eerdmans Publishing, Grand Rapids, 2003, pp. 52-53).