The textbook is devoted to the description of the successive change of Old Russian (X-XII centuries), all-Russian (XIII-XIV centuries) and Old Russian (XV-XVII centuries) periods in the history of the Russian language. Transformations of grammatical paradigms and categories are considered with particular attention; semantic reasons for their formation and morphological bases of all phonemic changes that took place over time are indicated; the main syntactic phenomena of the language are described in their connection with the formation of the Russian mentality.