The monograph is dedicated to the 400th anniversary of the birth of Archpriest Avvakum, the ideologist of the Old Believers, the pioneer of Selenga Dauria - Transbaikalia. Particular attention is paid to the history of the settlement of the territory of Transbaikalia by the Old Believers, the labor and military exploits of the descendants of Avvakum - Semey. The participation of Old Believers in armed conflicts of the XX century is highlighted. Based on the documents of the state archives of Irkutsk, Chita and Ulan-Ude, the pedigrees of several family family dynasties have been traced over a long period. The publication is addressed to historians, local historians, everyone who is interested in Russian history.