Knowledge Organization (KO) is about activities such as document description, indexing and classification performed in libraries, databases, archives etc. These activities are done by librarians, archivists, subject specialists as well as by computer algorithms. Knowledge Organization (KO) is about activities such as document description, indexing and classification performed in libraries, databases, archives etc. These activities are done by librarians, archivists, subject specialists as well as by computer algorithms. KO as a field of study is concerned with the nature and quality of such knowledge organizing processes (KOP) as well as the knowledge organizing systems (KOS) used to organize documents, document representations and concepts. There exist different historical and theoretical approaches to and theories about KO, which are related to different views of knowledge, cognition, language, and social organization. Each of these approaches tends to answer the question: "What is knowledge organization?" differently. LIS professionals have often concentrated on applying new technology and standards, and may not have seen their work as involving interpretation and analysis of meaning. That is why library classification has been criticized for a lack of substantive intellectual content. Traditional human-based activities are increasingly challenged by computer-based retrieval techniques. It is appropriate to investigate the relative contributions of different approaches; the current challenges make it imperative to reconsider this understanding. This paper offers an understanding of KO based on an explicit theory of knowledge.