Categories are used in Wikipedia to link articles under a common topic and are found at the bottom of the article page. Clicking the category name displays a list of articles in that category, below a list of sub-categories (categories in that category) (if any). Categories allow readers to navigate through Wikipedia and find related articles.

The bottom of the Wikipedia article Chicken eyeglasses. At the very bottom of the page, below the References, navigation templates and external links are a series of links. These links are the categories used on the page, which include: Category:Animal welfare, Category:Animal equipment, Category:Eyewear, and Category:Poultry farming. By clicking on the category link at the bottom of the page, readers can navigate the Category tree (see below).

Category tree

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 classificationsCategory:HistoryCategory:History by locationCategory:History by countryCategory:History of AustraliaCategory:History of Australia by locationCategory: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:

Category-diagram.png

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.