The concept of Knowledge Organization Systems (KOS) is introduced. The author describes the activities of the International Society for the Organization of Knowledge (ISKO), as well as the Basic Register of Thesauruses, Ontologies and Classifications (BARTOC) as the most representative registry of KOS. The KOS typology presented in the International Standard is discussed and a simplified KOS typology is proposed. The state of KOS in Russia is briefly characterized by the main categories: authority files, library classifications, classifications of scientific information, classifications of Internet resources, thesauruses, and ontologies. Conceptual reference models are considered separately as the most promising type of KOS. The main knowledge representation tools on the Semantic Web platform are listed. Tasks related to KOS are formulated within the framework of the Federal Project for the Development of Scientific and Technical Libraries, in particular, acquisition of the database of existing Russian KOS. Such a database, similar to the BARTOC database, will enable to monitor and compare existing KOS, and to decrease duplication of design projects. The “Russian KOS” database has to be designed compliant with the Semantic Web standards as the cloud of linked open linguistic data similar to the international resource. The author proposes the contents and structure of possible KOS for the future integrated system of sci-tech libraries.