any of the English Christians in the 16th and 17th centuries who wished to separate from the Church of England and form independent local churches. They were eventually called Congregationalists (Congregationalism). Separatists were most influential politically in England during the time of the Commonwealth (1649–60) under Oliver Cromwell (Cromwell, Oliver), the lord protector, who was himself a Separatist. Subsequently, they survived repression and gradually became an important religious minority in England.

One group of Separatists left England for Holland in 1608, and in 1620 some of them, the Pilgrims (Pilgrim Fathers), settled at Plymouth, Massachusetts. The Plymouth Separatists cooperated with the Puritans (Puritanism) (nonseparating Independents) who settled Massachusetts Bay (1630). In England the Puritans had hoped to purify the Church of England, but in New England they accepted the congregational form of church government in which each local church was independent. Thus, the churches of the Separatists and the Puritans became the Congregationalists of the United States.

A fundamental belief of the Separatists was the idea of the gathered church, which was in contrast to the territorial basis of the Church of England whereby everyone in a certain area was assigned to the parish church. Separatists believed that the foundation of the church was God's Spirit, not man or the state. Those who were definitely Christian believers, therefore, should seek out other Christians and gather together to make up a particular church. This belief was the basis for the autonomous local church of the Separatists, which became a principal tenet of Congregationalism.