The book in a popular science form presents the main milestones in the history of the Don Cossacks in the late Imperial period. The essay approach made it possible to consider in detail the most controversial issues of the development of the Don Cossacks in the second half. XIX - beginning. XX centuries: evolution of Cossack privileges; transformation of the system of military, village and zemstvo administration; the effectiveness of the Cossack service and its cost to the state and to the Cossack family. Special attention is paid to the description of the territory of the Don army, its military and district borders.