Unitarianism is historically a Christian theological movement named for its belief that God is one entity, as opposed to the Trinity, which defines God as three persons in one being; the Father, Son, and Holy Spirit. Unitarians believe that Jesus was inspired by God in his moral teachings and is a Savior, but he is perceived as a human rather than a deity. Unitarianism is also known for the rejection of several other Western Christian doctrines, including the doctrines of original sin, predestination, and the infallibility of the Bible. Unitarians in previous centuries accepted the doctrine of punishment in an eternal hell, but few do today. Unitarianism might be considered a part of Protestantism depending on one's stance or viewpoint; perhaps it being described a part of Nontrinitarianism, or both, is more accurate.
The Unitarian movement was not called "Unitarian" initially. It began almost simultaneously in the Polish–Lithuanian Commonwealth and in Transylvania in the mid-16th century. Among the adherents were a significant number of Italians. In England, the first Unitarian Church was established in 1774 on Essex Street, London, where today's British Unitarian headquarters are still located. Since the theology was also perceived as deist, it began to attract many people from wealthy and educated backgrounds, although it was only at the late second half of the 18th century that it started to gain some wider traction within Christendom. In the United States, it spread first in New England, and the first official acceptance of the Unitarian faith on the part of a congregation in America was by King's Chapel in Boston, from where James Freeman began teaching Unitarian doctrine in 1784, and was appointed rector and revised the prayer book according to Unitarian doctrines in 1786. In J. Gordon Melton's Encyclopedia of American Religions, it is classified among "the 'liberal' family of churches".