Descended directly from the Puritan or Congregational Church (now the United Church of Christ), the Unitarian religious movement and organization rose in the early 1800s in New England and continues today as the Unitarian-Universalist denomination.
Theologically "Unitarian" is named for its difference from "Trinitarianism," the orthodox doctrine that God has 3 aspects: Creator, Christ, Holy Spirit (or Father, Son, and Holy Ghost).
In contrast, Unitarians emphasize the oneness or unity of the divine.
This tendency to unity makes this denomination receptive to other religious traditions.
Another emphasis of Unitarian theology is rationality or reason, associating it with the Deism of the Revolutionary generation, and distinguishing it from the mystical or emotional identities of evangelical Christianity.
Most of the Transcendentalists of the American Renaissance were Unitarians or from Unitarian backgrounds. Ralph Waldo Emerson, the Transcendentalists' central figure, was a Unitarian minister before resigning over misgivings regarding Communion and public prayer. One of the main U-U churches in Houston is named Emerson Unitarian Universalist Church.
The Unitarian denomination has never been a populous denomination like the Baptists or Methodists, but it has been influential beyond its relatively small numbers because members tend to be highly educated.