Church of the Brethren is an Anabaptist church founded in 18th century Europe. Early believers structured their church based on the belief that Jesus wanted his followers to take part in "peaceful action, plain and compassionate living and a shared search for truth." For more information about the history of the Church of the Brethren and what they believe, consult their website at http://www.brethren.org/site/PageServer?pagename=visitor_about_history.
The Church of the Brethren Network of Genealogy and History Resources, http://www.cob-net.org/genchurch.htm, is a great place to start your search for Church of the Brethren ancestors. This website contains Congregational histories, photos, lists of libraries with Brethren collections, online databases, and other websites that provide information about the church.