The new book of authoritative St. Petersburg architectural historians examines the most significant architectural monuments of the Leningrad avant-garde - residential, public and industrial buildings of the 1920-1930s. This is the first edition specifically dedicated to the architectural heritage of the era in question. On the example of a number of characteristic monuments of the late XIX - early XX centuries, rationalistic innovations in the architecture of St. Petersburg Art Nouveau can be traced, anticipating the development of creative searches of the following decades. Addressed to specialists - art historians, architectural historians, local historians, teachers, students, as well as a wider readership.