The title 'Christian Brethren' is the name often given to a group of independent autonomous Christian congregations, which trace their origins back to Ireland in the 1820's. They are sometimes referred to as the Plymouth Brethren, or just Brethren, but some members dislike such titles because they suggest that they are a denomination. The Brethren have seen themselves as returning to an earlier tradition of worship as practiced in the New Testament, before the creation of formal churches and denominations.
The Brethren movement split in two in 1848 and the two wings are often referred to as the 'Open Brethren' and the 'Exclusive Brethren'. These titles continue to be used despite continued fragmentation and division, particularly in the 'Exclusive Brethren', in the years since. The movement in its various forms is a very 'broad church', but there are a number of distinctive doctrinal and ecclesiological features that characterize congregations in the Brethren tradition.
Exclusive groups (of which there are a number of different variations) have often adopted more tightly knit and centralized organizational forms. The independent and autonomous nature of 'open' congregations means that there is no centralized decision-making, and no hierarchy to police the Brethren for conformity; consequently there is much variety. Having said this, in many congregations across the world there is a clear sense of Brethren identity, a community of worship, and a similarity of belief. On the other hand, in recent years many independent 'open' congregations, which trace their roots to Brethren traditions, have changed, adapting to changing circumstances, and would be loath to describe themselves by the name 'Brethren'. The 'Brethren' have always had a strong evangelistic and missionary thrust. In consequence, there are 'Brethren' congregations in up to 130 countries in the world.