Unitarianism is a Nontrinitarian Christian theology which teaches belief in the single personality of God, in contrast to the doctrine of the Trinity (God as three persons). According to its proponents, Unitarianism reflects the original God-concept of Christianity. The movement has come to be associated with other liberal Christian beliefs as well.
The term Unitarianism (with an upper case “U”) customarily refers to a liberal Christian theology. The term unitarian (lower case “u”) is used descriptively to refer to anyone adhering to the teaching of the single personhood of God, a wide-ranging category that also includes many conservative evangelical branches which are not the subject of this article. They generally hold similar beliefs to most other evangelical Christians, apart from their rejection of the Trinity doctrine. This version of unitarianism is more commonly called Nontrinitarianism, rather than Unitarianism. There also are some nontrinitarians who, while holding God to be a single person, perceive Jesus to be God himself, and therefore they do not really fall into the usual unitarian category, which typically rejects the idea of Jesus as Almighty God. Instead see: Sabellianism, Oneness Pentecostalism, Monarchianism, Binitarianism, and The New Church.