This paper, first, brings to light some features of social ntworking, introducing the concept of inter-subjectivity, theory of distributed cognition and principle of emergence, also mentioning the concept of information fluency for library communities. Secondly, this paper briefly reviews current library applications of social networking in the world level as well as status in Korea, such as twitter (Micro-blogging/ Presence updates), delicious (Web Resources Sharing), librarything (Cataloguing thru Social Networking: social cataloging web application for storing and sharing personal library catalogs and book lists) and library applications of some mash ups. Widgets, Libraries on FriendFeed and Google Profiles of libraries are also mentioned. Third, open source software platforms are also briefly reviewed in terms of library use. In this, a new paradigm shift of information organization in library field is mentioned: attempts are being made to move from a web of documents to a web of data. Popular Rdf Vocabularies are also briefly introduced. In this, FRBR vocabularies are specially emphasized. Since these are relatively not known to the specialists in other areas. FRBR can easily be implemented as an RDF vocabulary, that could be used to create a universal Linked Data library network. Some library related Linked Data projects are also briefed. Some notions of semantic interoperability are also briefed. Lastly,proposed models for Library apllications of social networking are suggested. Some implications of the use of library applications of social networking are also briefed.