The paper analyzes home studies of the 19th – early 20th centuries, dedicated to religious non-Orthodox movements in the Russian Empire – the Molokans and the Russian Judaizers. The topicality of the work stems from both insufficient research of the history of these movements in modern religious studies and the extreme lack of works dealing with the pre-revolutionary historiography of the problem. The study reveals the presence of a rich and multifaceted literature on Molokans and Subbotniks, which was created by the officials, church authors, scholars, public figures and private observers. The authors considered diverse aspects of the sectarian movements, so that their works are an important source for the research of Russian religious dissenters and at the same time – a serious contribution to the development of religious studies in Russia. Historiographic analysis traces the formation of the terminology denoting religious dissidents. At first sectological discourse clearly lacked clarity and relevance in the names of the movements as well as in different currents within them. Subsequently the meanings of various terms were clarified, but till the end of the 19th century some researchers still hadn’t been strictly distinguishing both religious movements and their designations. The social status of the authors, their professional activities, political and cultural preferences, sometimes ethnic identity determined (though not always directly) the diverse discourses of perception of religious nonconformists. They varied from intolerance to outright sympathy. During the period under consideration the evolution of concepts of the sectarians as well as interest in them correlated with sociopolitical and religious processes in the country and also with changes in social and research paradigms.