The Dewey Decimal Classification system (DDC) is the world’s most popular library classification system. The 23rd edition of the DDC was published in 2011. This second edition of The Theory and Practice of the Dewey Decimal Classification System examines the history, management and technical aspects of the DDC up to its latest edition. The book places emphasis on explaining the structure and number building techniques in the DDC and reviews all aspects of subject analysis and number building by the most recent version of the DDC. A history of, and introduction to, the DDC is followed by subject analysis and locating class numbers, chapters covering use of the tables and subdivisions therein, multiple synthesis, and using the relative index. In the appendix, a number of academically-interesting questions are identified and answered.