At a time when the fractious legacy of the Protestant Reformation is coming under new scrutiny, Anthony Siegrist explores the implications of ecumenism for believers' baptism. Writing from within the tradition of the Radical Reformation, he challenges dominant ecclesiological assumptions and argues that this central practice needs to be reconstrued. Siegrist works constructively to develop a concrete account of believers' baptism that attends closely to the dynamics of divine initiation. Siegrist deliberately stretches the traditional Anabaptist conversation to include not just expected voices like Yoder and Marpeck, but also luminaries from the broader Christian tradition; Barth, Bonhoeffer, and a variety of ancient sources are creatively engaged. The intent of Participating Witness is eminently practical, but its argumentation is carried out with theological rigor.