It is a commonplace statement of modern historiography that aft er the transfer of the Don Cossack Host from the jurisdiction of the Ambassadorial Prikaz to the Military Collegium in 1721 it completely lost its autonomy. In recent years, however, such an assessment of the infl uence of the Emperor’s Edict of 3 March 1721 on the position of the Don Cossacks is reconsidered. Their status in the post-Petrine period can be clarifi ed through the study of personal letters of the Russian autocrats to the Don. The research aims to show Empress Anna Ioannovna’s attitude to the Don Cossacks on the basis of the letters she sent during the Russian-Turkish war (1735–1739). The letters as a form of correspondence between the supreme power and the Don Cossacks’ community are examined in the context of the historical-typological approach to the study of historical sources, which involves the formulaic analysis. The article deals with the following topics: the place of letters in the system of legislative and clerical materials of the Russian state and the Russian Empire, the requirements to the letters, established by Peter I in the course of his reforms of state administration, the procedure of creation of letters in the personal offi ce of the Empress (Cabinet of Ministers) and the Senate, and peculiarities of letters, sent to the Don. Th e research of the imperial letters of 1735–1739 leads to the conclusion that during this period the Don Cossack Host was in a state of “special subjection”: on the one hand, like during the rule of Peter the Great, it was directly subordinated to the autocrat, while enjoying at the same time a certain degree of independence, on the other hand, it received letters of diplomatic character from Anna Ioannovna. The letters of 1735–1739 reveal the principle of mutual benefi t as the basis of relations between the Russian supreme power and the Don Cossack Host. This principle was declared inviolable not only in Anna Ioannovna’s correspondence, but also earlier, in the Tsar’s letters in the sixteenth and seventeenth centuries. Radical changes in relations between Russian authorities and the Don Cossack Host started in the 1770s.