In the proposed article by Viktor Sokolov «Professional activities of a librarian in medieval Europe’s monastic libraries: characteristics, functions, peculiarities» the information concerning the activities of a librarian in Western European monastic libraries in the middle ages is analyzed and summarized. The relevance of this study is due to the need to study the specifics and development of the functional duties of monastic librarians, which have not been studied before, against the background of the formation and evolution of monastic libraries in the Early middle ages. The purpose of this article is to identify and characterize the features of the activities of librarians of monastic libraries in medieval Europe (mainly Western). The methodology of this scientific work consists in the application of both general scientific research methods (description, comparison, analogy, deduction, induction, analysis, etc.) and historical (historical-comparative, historical-typological, chronological, etc.) methods. Methods of terminological analysis, analysis of dictionary definitions, etymological and word-formation analysis, bibliographic and other research methods were also used. The article explores the main areas and areas of activity of a librarian in Western European monastic libraries, as well as some features of the development of book and library business in monasteries through the prism of the functional duties of a librarian. The content and significance of his professional activities in the dissemination of reading, education, development of book and library business are analyzed. The study made it possible to reveal the peculiarities of the interpretation of the terms that determine the activities of the librarian of Western European monastic libraries in the middle ages, in particular, the term «armarius» in modern book science and library research. The main factors and features of the formation of the meaning of the term «armarius» in the process of becoming a professional activity of monastic librarians are revealed. The scientific novelty of the work lies in expanding the understanding of the professional activities of the librarian of Western European monastic libraries in the period, mainly, the early middle ages and revealing the significance of his activities in the development of not only book and library science, but also the spiritual culture of the middle ages as a whole. The study shows that monastic librarians played an important role in organizing systematic reading among monks – both individual (including for educational purposes, in the form of obedience) and collective – using the method of reading aloud to familiarize themselves with the content of certain (predominantly theological) books. The position is confirmed that for the monastic librarian, a wide education, erudition and knowledge of books was considered an indispensable feature of his professionalism. Performing professional tasks at the proper level required from the monastery librarian certain analytical abilities in working with text, knowledge of several foreign languages (including ancient ones), detailed content of religious books, the ability to describe books and compile catalogs, as well as perform various functions that require conscientiousness, accuracy, ingenuity, etc. The article shows that the monastic librarian had to organize the work of the library at the appropriate level and monitor the proper use of books by the monks, as well as monitor their reading needs. The librarian not only supervised the work of the monastery library, ensured the preservation of books and control over their proper use, but also actively engaged in book business through the management of the scriptorium, controlling all stages of book creation. Conclusions. The activity of the monastic clergy, including monastic librarians, spreading the Christian doctrine, thereby contributed to the spread of literacy and reading among a certain part of not only the monks, but also the population as a whole. Gradually, writing became an integral part of monastic life, where books and libraries occupied an important place. The decisive place in these processes was occupied by the librarians of the monastery libraries as the keepers of book collections and bearers of the spiritual and educational mission, book culture among the clergy and laity.