Objective. The philosophical foundations that support the use and development of the Dewey Decimal Classification (DDC) were explored. Design/Methodology/Approach. Different primary and secondary sources were reviewed to analyze the theories and ideas that founded the DDC. Results/Discussion. The DDC is a system that bases its scheme on the ideas put forward by Bacon and Hegel. However, its operation is due to what has been called “Decimal theory”. Conclusions. The DDC is a system of library organization that is influenced by modern scientific ideas in the nineteenth century, and should not be seen as a simple tool for classifying books. Originality/Value. New bases are given to Librarianship as a science, based on the theoretical study of the DDC and the organization of knowledge associated with it.