The Open Brethren, sometimes called Christian Brethren, are a group of Evangelical Christian churches that arose in the late 1820s as part of the Assembly Movement within the Plymouth Brethren tradition. They originated in Ireland before spreading throughout the British Isles, and today they have an estimated 26,000 assemblies worldwide.
The Open Brethren form independent, autonomous assemblies and the name "Open" is given to them to distinguish them from "Exclusive Brethren", with whom they share historic roots. The division of the Plymouth Brethren into the Open Brethren and the Exclusive Brethren took place in 1848. Open Brethren are also commonly known as "Plymouth Brethren", especially in North America. Many Open Brethren outside North America, however, are unwilling to use the "Plymouth Brethren" designation because it is associated with the Exclusive Brethren, particularly the Plymouth Brethren Christian Church, which is known for its rigid interpretation of the doctrine of separation from the world.