Wikipedia's main categorical index system is automatically generated from information (category tags) at the bottom of each article. The category system has 3 top-end pages, which are:

• Categorical index – an index of major categories, arranged by subject - that section of the page is an exception to the category autogeneration rule, as it is crafted by hand.
• Category:Categories — the highest level or "root" category in Wikipedia - its autogenerated entries are listed at the bottom of the page.
• Category:Contents — the category equivalent to this page.
• Category:Articles — the category in which all article category systems are located.

Wikipedia's other broad categorical indices are:

• List of Dewey Decimal classes — lists the top two levels of this library classification system
• Library of Congress Classification — this article provides a reflection of its own deep linkage structure
• Wikipedia:Outline of Roget's Thesaurus — articles organised into a system based on six classes, with thousands of branches, following Roget's system

Spoken articles

• Category:Spoken articles — articles that are available as spoken word recordings