Relations among believers of different religions are often characterized by conflict and disharmony. The interreligious conflict and disharmony are not in line with the doctrine and religious mission itself, which on the contrary promote peace and harmony. If the undesirable opposite happens, it means there is a gap between the normative teachings with the empirical reality. Why does that happen? This article reveals the issues related to the Christian-Muslim relations in Indonesia over a period of time along with the factors underlying the disharmony of Christian-Muslim relations in Indonesia. The method used to analyze this problem was the historical-sociological approach. This study concludes that the Christian-Muslim conflict in Indonesia is triggered by external rather than (internal) problems such as political and economic issues as well as the shalow understanding of the believers themselves.