It has been long time for the introduction of marketing concepts to libraries. Some of the concepts, however, have misunderstood and inappropriately explained in them. The effort of this article is to define the core meaning of library marketing. Public libraries need marketing measures undoubtedly. As a result, it needs library staffs to pay more attention to this issue. This article begins with a general survey of external environment of public libraries and the difficulties for the libraries when they implement a marketing plan; followed by the main topic-to clarify some of the concepts as well as the principles concerning library marketing. Several methods and instruments for practical use are also mentioned.