First Church in Boston is a Unitarian Universalist Church founded in 1630 by John Winthrop's original Puritan settlement in Boston, Massachusetts. The current building, located on 66 Marlborough Street in the Back Bay neighborhood, was designed by Paul Rudolph in a modernist style after a fire in 1968. It incorporates part of the earlier gothic revival building designed by William Robert Ware and Henry Van Brunt in 1867. The church has long been associated with Harvard University.

Congregationalism in the United States consists of Protestant churches in the Reformed tradition that have a congregational form of church government and trace their origins mainly to Puritan settlers of colonial New England. Congregational churches in other parts of the world are often related to these in the United States due to American missionary activities.