By the end of 1890s, Grabar had established himself as an art critic. In 1902, he joined Mir Iskusstva, although his relations with its leaders Sergei Diaghilev and Mstislav Dobuzhinsky were far from friendly. In 1910–1915, Grabar edited and published his "opus magnum", the "History of Russian Art". The "History" employed the finest artists and critics of the period; Grabar personally wrote the issues on architecture that set an unsurpassed standard of understanding and presenting the subject. Concurrently, he wrote and published a series of books on contemporary and historic Russian painters. In 1913, he was appointed executive director of the Tretyakov Gallery and launched an ambitious reform program that continued until 1926. Grabar diversified the Tretyakov collection into modern art and in 1917 published its first comprehensive catalogue. In 1921 Grabar became the first professor of "Art restoration" at the Moscow State University.