Categories are not displayed in the mobile version. Mobile users can click "Desktop" at the bottom of a page to see the desktop version with categories. Registered users can enable Advanced mode which includes a "Categories" button.

All of the categories form a hierarchy, although sub-categories may be a member of more than one category. An example of a small part of this hierarchical structure looks somewhat like this:

    Category:Main topic classifications
                      ↓
              Category:History
                      ↓
       Category:History by location
                      ↓
       Category:History by country
                      ↓
      Category:History of Australia
                      ↓
     Category:History of Australia by location
                      ↓
Category:History of Australia by state or territory
                      ↓
      New South Wales, Queensland, etc.

The actual relationship is more complex since a category may appear as a subcategory of several other categories. The actual relationship of part of the category structure looks like this:

The uppermost category in the hierarchy is Category:Contents. From here all other categories branch out, including those that are used for the maintenance of Wikipedia.

If an entry in a category is shown in italics it is a redirect to an article of a different name or a section of an article that contains information about that particular subject.