The author examines a composer's creative process with reference to the analysis of philosophical and aesthetic, psychological, culturological and musicological works of the 19 - early 20th century along with the reflections of composers themselves, allowing the listener into their sacred creative laboratory. The article reveals the most significant peculiarities of a composer's creative process as related to the general cultural tendencies of different epochs. Special attention is paid to the unique features of the creative process of 20th century composers I. Stravinsky, S. Prokofiev, A. Webern, A. Schnittke, S. Slonimsky, etc.