Based on primary and secondary sources, this study evaluates Nommensen's basic beliefs, his missionary methods, collegial spirit, and his strategy from missiological, ecclesial and sociological perspectives. Face-to-face interviews with living relatives, native Bataks, and German colleagues have enabled the author to shed light on his methods, style, and achievements as a missionary. In dealing with his missionary endeavours in the context of his particular setting (among the Bataks of North Sumatra in Indonesia), the biography notes his interdependence in working with others and the kind of indigenization of the Christian faith he and his co-workers brought about.