The present book is a modest attempt to fill the void and describe in detail the nuts and bolts of Dewey Decimal Classification and abate the problems faced by the students as well as the library professionals. Lack of sound theory as well as the different instructions makes it inevitable to be supplemented with a manual in order to grasp the tools of number building. The book is divided into five chapters that discusses in detail each tables (1) to 6) and main classes (100 to 900) with about 400 practical cases of number building for the construction of call numbers. For the first time an attempt has been made to discuss the practical strategies of DDC23 with so many practical cases. The book is targeted towards the Library & Information professionals as well as the students at various levels pursuing Library Science who want to clasp the essence of DDC23.