The analysis of the book by M.V. Seslavinsky “Russian Book Rarities of the 20th century: 333 Selected Books” (Moscow: Pashkov Dom, 2016. 381 p.) is presented in the context of a problem of allocation of rare books and book monuments as a special category of library collections. It is shown that M.V. Seslavinsky, basing on the best traditions of Russian bibliophile literature, suggests his own approach to the allocation of the book rarities, based on the combination of quantitative criteria and cultural significance, and also taking into consideration the interest to the edition in the modern antiquarian book market. Proposed by M.V. Seslavinsky list of book rarities, released mainly in the first third of the 20th century, reflects the system of values of the modern Russian bibliophile community, a prominent representative of which is the author of the reviewed book. The publication contains rich illustrative material and the author’s comments. The principles of the selection of rare books and the list of rarities by itself deserve special attention of experts working with book monuments, collectors and acquisitions librarians.