This study examines the issues of phonetics and morphology, as well as the graphics and spelling of the Cathedral Code of 1649. - the most important monument of the Moscow command language of the late forties of the XVII century. The book gives a general description of the features of writing and the grammatical structure of the language of the Laid Book compared, on the one hand, with the old Moscow vernacular of that time, and on the other - with the norms of the Russian literary language of our days and in connection with the history of this book.