The article is focused on the sources of education for music theorists and composers in Russia. It examines the question, for the preparation of what kinds of musicians the major studies of “Music Theory” were directed: whether it brought up instructors of music theory disciplines, or provided for education for composers? This question is legitimate already because Piotr Tchaikovsky in his aspiration to become a composer wrote a request to enroll into a special class of music theory at the St. Petersburg Conservatory, while in his diploma among the enumerated disciplines that of “Composition” is lacking. The historical documents, preserved in the archives of St. Petersburg, Moscow and Klin, bear witness that the music theory students were taught according to one program of preparation of composers. The entire process of study, in which the theory and practice of musical composition were placed on par with each other, was directed towards the achievement of this aim. The sources of the given concept lie in the German practice of teaching professional musicians, first of all, in the theoretical pedagogical system of Adolf Bernhard Marx. His pupil and follower, Nikolai Zaremba became the founder of Russian conservatory education, which was based on Marx’s system. And Zaremba’s pupil Tchaikovsky transferred the principles of parity teaching of the theory and practice of composition to the Moscow Conservatory. How these principles were carried out in the teaching of the disciplines “Harmony,” “Counterpoint,” “Form and Fugue,” “Orchestration” and “Composition” is examined in the article on concrete examples, which are the archival sources: the textbook “Forms” by Zaremba’s pupil Vasily Safonov and the rough drafts of the programs for music theory disciplines made by Tchaikovsky. Keywords: first Russian conservatories, education for music theorists and composers, musical source studies, Adolf Bernhard Marx, Nikolai Zaremba, Piotr Tchaikovsky.