Through the bibliometric approach and citation analysis, this study analyzes the disciplines and subjects of literature citing important information science journals during the period from 1998 to 2010. The four information science journals under study include Journal of the American Society for Information Science and Technology, Information Processing and Management, the Journal of Information Science, and the Journal of Documentation. The Ulrich’s Periodical Directory, Library of Congress Subject Headings retrieved from WorldCat and the LISA database were used to identify the main classes, subclasses, and subjects of citing journals. We also indentify and analyze the highly citing journals, the main classes and subclasses of citing journals for the four journals under study as well as highly cited subjects in journals related to library and information science. Overall, the knowledge flow out of the domain of information science mainly includes information science itself, and also science and technology at a lower percentage. Moreover, there are minor outputs for various other subjects. The comparison of knowledge flow into and out of the domain of information science reveals the main knowledge flow is into information science itself. This comparison also reveals significant knowledge flow from computer science to information science.