Congregationalist polity, or congregational polity, often known as congregationalism, is a system of ecclesiastical polity in which every local church (congregation) is independent, ecclesiastically sovereign, or "autonomous". Its first articulation in writing is the Cambridge Platform of 1648 in New England.

Major Protestant Christian traditions that employ congregationalism include Quakerism, the Baptist churches, the Congregational Methodist Church, and Congregational churches known by the Congregationalist name and having descended from the Independent Reformed wing of the Anglo-American Puritan movement of the 17th century. More recent generations have witnessed a growing number of nondenominational churches, which are often congregationalist in their governance.

Congregationalism is distinguished from episcopal polity which is governance by a hierarchy of bishops, and is also distinct from presbyterian polity in which higher assemblies of congregational representatives can exercise considerable authority over individual congregations.

Congregationalism is not limited only to organization of Christian church congregations. The principles of congregationalism have been inherited by the Unitarian Universalist Association and the Canadian Unitarian Council. Most Jewish synagogues, many Sikh Gurdwaras, and most Islamic mosques in the US operate under congregational government, with no hierarchies.