Objective: The aim of this study is to investigate the theories and theoretical studies in the field of library classifications and historical context of them in order to identify the approaches and developments in the field of classification.Methodology/Approach: The method of research was literature review and investigation of the theory of classifications.Results: The main theories in the designing of library classification systems that have been proposed include: Theory of Literary Warrant, Theory of scientific and educational consensus, Theory of phenomenon based knowledge organization classification, theory of integrative levels, Theory of Evolutionary Order, Information Coding Classification, and Universal Binary Classification.Conclusion: Current approaches in the knowledge organization have been shifted from static classification to dynamic, from universe of knowledge to universe of concepts and from deductive approaches to inductive approaches.Keywords: Theory of Literary Warrant, Theory of scientific and educational consensus, Theory of phenomenon based knowledge organization classification, theory of integrative levels, Theory of Evolutionary Order, Information Coding Classification, and Universal Binary Classification.