This thesis is a contribution to a hitherto neglected area of research: The African Pentecostal Churches, that do not belong to those called African Indigenous Churches (AICs). It is a case study from the perspective of southern Burundi, the periphery of the ancient kingdom. The Pentecostal Movement in Burundi was born in the encounter between Swedish Pentecostal missionaries and the population in the southern part of the country. This study highlights what happened in that encounter. The thesis consists of six parts. The first is a survey of the Pentecostal Movement in Sweden. The diachronic structure of parts two to five focuses on the development within the Burundian Pentecostal Churches and their relationship to the Burundian society 1935-1960. In the sixth part the diachronic approach is augmented by structural analyses, showing how aspects in the Pentecostal Movement developed. The Pentecostal missionaries accepted in part the traditional world view, the belief in a spiritual world and non-rational explanations to misfortunes in life. They encouraged the Burundians to do spiritual experiences, and especially the baptism in the Holy Ghost. The Burundian evangelists and church elders played a decisive role. It was their task to reformulate the Pentecostal message in Kirundi, which was not spoken by the missionaries. They moulded the message into a Burundian Pentecostal message, at the same time respecting the teaching of the early missionaries. They succeeded in doing that so well that the Pentecostal Movement became a popular movement, in certain places the dominating Christian denomination, in spite of the parallel work done by the Catholic Church, encouraged and supported by the Belgian state. This thesis builds on material taken mainly from unpublished sources from archives in Burundi, Sweden, Rome, Great Britain and Denmark. These are supplemented by interviews, most of them made by the author.