Ensuring accessibility of library services is one of the most urgent tasks of modern librarianship. The concept of “accessibility” which is actively used in the regulatory framework for librarianship and in the works of library scientists, at the same time remains insufficiently substantiated and developed. The article presents the options for the disclosure of the concept of “accessibility” and correlates the concepts of “access” and “accessibility”.In the regulatory framework in dictionaries and reference books on librarianship, the term “accessibility” started to be used relatively recently. The UNESCO Information for All program, as well as organization of the Open Access Movement to scientific information, played an important role in the awareness of the world community of the need for universal access to information. The beginning of the 2000s in Russia is a period of active study of electronic libraries, for which the concepts of “access”, “accessibility” and similar are an important component. During this period, there has been increasing the importance of the issue of barrier-free environment for people with disabilities, where the concept of physical accessibility is the key one. In librarianship documents, the term “accessibility” is also used as physical opportunity to obtain information.At the moment, this concept is introduced in the State Standard of Russia GOST R 7.0.103-2018 “Library and Information Services. Terms and Definitions”. The concept reflects the general trend of using the term “accessibility” mainly in the digital environment; however, the concept of “accessibility” is much broader and is not limited only to access to electronic resources and physical accessibility of the library. The concept of “accessibility” should be considered through information barriers (physical, assortment, navigation and search, deunification), since overcoming them will allow the library to become as accessible as possible. The problem of accessibility of library services has several aspects, and it is important that the scientific community and librarians realize the complexity of this problem and focus their attention not only on ensuring the physical accessibility of the library, but also on removing other information barriers.