Our society is rapidly changing into information society, where the needs and requests of the people on information access vary vigorously depending who they are. Library's mission has been and still is to provide its users, or patrons, with the most appropriate information. Libraries have to know the profiles of their patrons, in order to achieve such a role. The aim of library marketing is to develop methods based on the library data, such as circulation records, book catalogs, book-usage data, and so on. In this paper we discuss the methodology and importance of library marketing at the beginning. Then we demonstrate its usefulness through some examples of analysis methods applied to the circulation records in Kyushu University and Gwacheon Library, and some implication that obtained as the results of these methods. Our research is a big beginning toward the future when library marketing is an unavoidable tool.