Cataloguing the Internet resources is being compared to cataloguing library resources. Social tagging is one of the methods of systematizing the Internet contents. The researchers have been deliberating for several years whether this method is useful for libraries, how it’s usefulness can be increased, and how to eliminate it’s shortcomings, to make it an equal tool in library information-retrieval systems. The author presents systematic review of current research on this topic, and proposals of folksonomy transformation into controlled tagging systems. She also offers a thesis concerning a tendency of folksonomy development into facet thesaurus, comparing tags to uniterms’ system.