The Radical Holiness movement deeply impacted not only emerging Holiness and Pentecostal denominations but existing churches. This impact was especially felt by the so-called Peace Churches of Friends, Mennonites, and the Church of the Brethren. This essay explores the understudied Brethren experience. It describes Brethren mission theory in the Social Gospel era and its relationship to currents in the broader Protestant world. While denominational mission board members followed a more moderate course, pastors and missionaries nurtured at Bethany Bible School, later Bethany Theological Seminary, drew on Radical Holiness currents. The most important was Anna Beahm Mow, missionary to India, professor, and popular evangelical author. For Mow the essence of the Christian or surrendered life was living a life devoted to and shaped by Christ, not support for programs or institutions.