Our contemporary Arkady Vasilyevich Sokolov (1934–2023) specialized in many disciplines within the documentology sphere, namely library science, bibliography, informatics, noocommunicology, etc., and documentology, in particular. The author focuses on this aspect of Sokolov’s work. His interest in documentology raised naturally from informatics, with his starting point in 1962. Professionally engaged in information search, Sokolov explored the nature of information, which finally culminated in the monograph “The philosophy of information” in 2010. In those days library scientists were willing to become the part of information science persuading – themselves, first of all – that that the library science was an information discipline. Sokolov’s many and rather substantial arguments were contradictory. He criticized reasonably the interpretation of library functions in the 1994 Federal Law “On librarianship” by emphasizing that it was a mistake to set the information function against the others. However, instead of calling for adequate statement functions he tried to rationalize this inaccuracy. Similarly, the inappropriate approach he applied to the comparison of “information” and “document”, “document” and “book’ concepts. Meanwhile, Arkady Sokolov has expanded significantly the field of documentology by introducing the concept of documentosphere into the philosophy of documents. He started developing the concept of Bibliologos that encompasses the whole field of documentology. The author concludes that Arkady V. Sokolov’s contribution to documentology is great and undeniable.