The Dewey Decimal Classification (DDC), used in 200,000 libraries across 140 countries, has entered a new age, primarily maintained today as a continuously revised electronic system rather than an occasionally updated set of print volumes. Its editors have added newly emerging topics and made it an increasingly faceted, semantically rich, modern system. Simultaneously, the editorial process has become democratised and more responsive to global needs. A Handbook of History, Theory and Practice of the Dewey Decimal Classification System is a comprehensive, practical guide to today's DDC. Coverage includes: a brief history of the system, its editors, and its development specialized examinations of specific parts of the classification extensive guidance on number building, with many examples a WebDewey-specific chapter, covering the system's benefits and features concise summaries of primary takeaways, a glossary, and extensive bibliography. This book will be an indispensable guide to 21st-century DDC, an essential companion for DDC classifiers, and accessible for students and continuing learners as well.