Form of church government adopted by those Protestant Christians known as Congregationalists, who let each congregation manage its own affairs, like the people of the Old Testament. The first Congregationalists established themselves in London and were called the Brownists after Robert Browne, who in 1581 defined the congregational principle. They opposed King James I and were supporters of Oliver Cromwell. They became one of the most important forces in the founding of New England.
During the 17th century they joined with Puritans in opposing the Church of England hierarchy. Many fled to Holland to avoid persecution, and in 1620 Congregationalists who left Holland on the Mayflower founded Plymouth Colony in Massachusetts. The early Congregational churches in New England were distinguished for their devotion to education—founding Harvard, Yale, and most of the other older private colleges of the region. During the 19th century, Congregationalists lost their semiestablished status in New England, and many congregations turned to Unitarianism, but Congregationalism spread to the Midwest and elsewhere. In 1959, Congregationalists merged with several other groups to form the United Church of Christ.

System of beliefs and church government of a Protestant denomination in which each member church is self-governing.