This study is to research quintessence of information service in the libraries by interpreting ‘Information' as it is ubiquitous. For the purpose, it investigates and analyzes information behaviors of the libraries in information-cultural history. The meaning of ‘ubiquitous' is understood as a practice that everything we need should be inherent in our lives for its usefulness and effectiveness. Information is intrinsic in our lives and the libraries, information management systems, have been evolved by extending the intrinsic value of information, ‘ubiquity'. Human being's history results from information behaviors and the meaning of the libraries consists of production, accumulation, organization and distribution of the libraries. It should be recognized that the ultimate purpose of the library services is for their users. Consequently information systems and technological networks in the libraries should be focused on applications and inherence for the purpose. Model studies of the libraries should be developed to user-centered information services that substantialize the interpretation of information, as it is ubiquitous. This study is a trial for defining the quintessence of the libraries. Furthermore, it provides foundation of understanding what the libraries are.