The Congregational churches trace their origins back to the separatist "Pilgrims" who established Plymouth Colony in 1620, and to the Puritans of the Massachusetts Bay Colony, who landed in 1629 and 1630 and settled Boston, whose organizing principle is Congregationalism. The UCC therefore unites one of the earliest Protestant denominations in the United States with various other Reformed traditions that sprang up in the United States in the 1700s and 1800s.
The UCC uses four words to describe itself: Christian, Reformed, Congregational, and Evangelical. This gives individual congregations a great deal of freedom.
The motto of the United Church of Christ comes from John 17:21: That they may all be one. The UCC places little emphasis on doctrine, emphasizing instead freedom of individual conscience, and as a whole is considered a liberal Christian denomination in the United States, although some individual UCC congregations can be very conservative.