This book simply aims to introduce the students to the process of assigning and especially synthesising the class numbers by the 19th edition of the DDC. The book is student-oriented and only aims at them. The chapters and the examples have been graded and no background, whatsoever, has been assumed on the part of the users. Though aimed at the beginner, yet it provides a complete course to train the students in the techniques of subject analysis and number building involving the use of seven auxiliary tables and multiple synthesis. The graded process of number building may mirror before the students the increasing edition by edition faceted nature of the system. To avoid verbosity the number building has been depicted through equations and facet formulae. Another aim is to be simple and clear. Many examples have been taken from 21st century literature; its theory and bibliography have been updated to the latest 23rd edition (2011) with an appendix on abridged edition (2012). It charts the course of the DDC from the 19th to 23rd editions.