This study explores the history of the Toba Batak community in the city of Medan from1912 to 1965. The Toba Batak have traditionally lived in the rural interior highlands ofSumatra. In this region, their specific ethno-religious identity was developed. Thecrucial factor in the process was the activities and the theological convictions of theGerman Rhenish mission on which the Toba Batak themselves had a significant impact. During the first few decades of the 20th century the Toba Batak began to migrate to the plantation region on the east coast of Sumatra and its commercial entrepôt Medan.In this region, where the Malay Muslim culture was the local dominant culture, theystrove to fulfil their cultural ideals, among which the ideal of harajaon (kingdom) iscentral. The main analytical question pursued is: How did the Toba Batak ethno-religious identity develop in Medan, within the framework of the ethnic, religious, social andpolitical currents in the city? This question is analysed in terms of their changing relations to their area of origin,the interaction with other groups in Medan and the efforts of the Toba Batak to buildup their own organisations. The main focus is on the development of Christiancongregations, but the analysis also takes voluntary, political and women's organisationsinto account. The changing conditions for local ecumenical co-operation are alsoexplored. A wide selection of sources is used, such as missionary reports and correspondence, Dutch colonial records and Toba Batak written and oral sources. Most of these sources have not or only partly been employed in previous research.