Theory is the eye of practice, while basic theory is the pupil of the eye. The development of basic theory is the cornerstone and the barometer of the development of a subject. Since the reform and opening up in 1978, the basic theories of library science and information science have been developing continuously, bringing forth a large number of research achievements, which include both the introduction of foreign advanced theories and the original theories aiming at China’s own situation, both the research on the discipline object and the summary of research paradigm, and both the formation of methodology and the induction of basic principles. In the past years, there have been both consensus and controversy in the study of basic theories of library and information science. Through these studies, the understanding of topics has been deepened and the summary of theories has matured, which has laid a good foundation for the development of the discipline. Library science and information science have their own development paths and characteristics as well as some common theoretical basis. In the process of development, there have been constant overlapping and merging, so that the growth momentum of new disciplines represented by information resource management has come into being. This chapter systematically summarizes and reviews the course of basic theory research of library science and information science and briefly reviews the theory of information resource management in combination with the development of the times.