This article presents the research of Orthodox priests who studied the religious ideas of the peoples of the Russian Empire. Their works, both published and in manuscript, can be classified into five main groups: studies dealing with Abrahamic religions; studies of other world and national religions; studies of religious dissidents (Christian sects and Judaizers); works on the traditional beliefs of the native peoples of the Volga Region, the Urals, Siberia, and the Caucasus; and works on popular religiosity.