- OCLC Online Computer Library Center - Order from the authority that owns the copyright to the Dewey Decimal Classification System the book or online version of the DDC Dewey Decimal Classification volumes.
- Summaries - OCLC’s online Brief Introduction to the Dewey Decimal Classification System, followed by the Summaries on page 9 of that pdf document.
- Library of Congress Online Catalog - To find a Dewey number for any item in the Library of Congress\' online catalog, click Basic Search. Search by Title or Author. Click the Full Record tab, and scroll down to see the Dewey classification number.
- Appleton Public Library’s Dewey Guide - A library’s alphabetical list of topics and their Dewey numbers.
- Do We Really Know Dewey? - Simplistic introduction to Dewey, possibly for students.