The author of this article aims to determine the historical framework of the formation of the confessional group of the Chuvash Muslims, its geographical delimitation and demographical dynamics. Her study is based on documents coming from central and regional archives as well as from the literature published on related subjects in Russia and abroad. She depicts the history of Islam in the Volga region, assessing that in the sixteenth century Muslims fortified their positions there, a great part of them being incorporated into a Turkic cultural environment with strong presence of Islamic culture, and the Chuvash themselves being involved in mass conversion to Islam. However, according to the author’s assessment, the religious beliefs of the majority remained unchanged, characterized by the author as a “Muslim-pagan syncretism.” Considering geopolitical change, the author also stresses the decrease of Muslim influence in the region from the mid-sixteenth to the late eighteenth century. More favourable conditions were created for Islam only after Islamic religious practice was tolerated from 1773 onwards, and Tatar economic and cultural influence increased along the nineteenth century among Chuvash populations. The combination of these factors allows the author to sketch a balanced picture of conversion to Islam — or to Christianity — among varied Chuvash populations in the nineteenth and early twentieth centuries.