The article deals with scientific literature and periodicals referring to the Udis and which were written in the period that followed their joining the Russian Empire (XIX - beginning of the XX century). The reasons to study the Udis ethnos by scientists of different countries, including foreign countries, are found out. These sources deal with the Udis, describe their economic activities, household and everyday life, give their classification. The author makes the conclusion about the importance of this period in the Udis history, as the first knowledge about the Udis and first research of them refer to this period.