The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Hatnote templates (7 members)
- Hawks (1 member)
- Hedgehogs (4 members)
- Heroes (14 members)
- Humans (2 members)
- Hybrids (1 member)
- IDW Publishing (1 member)
- IDW Publishing characters (6 members)
- IDW Publishing groups (2 members)
- IDW Publishing locations (1 member)
- IDW Publishing moves (1 member)
- IDW Publishing transformations (1 member)
- If-then-else templates (1 member)
- Image wiki templates (1 member)
- Image with comment templates (3 members)
- Immortals (1 member)
- Infoboxes (10 members)
- Inline hatnote templates (1 member)
- Inline templates (1 member)
- Internal category-link templates (3 members)
- Internal template-link templates (4 members)
- Inventors (4 members)
- Islands (1 member)
- Knights (1 member)
- Knuckles' Chaotix (3 members)
- Knuckles (TV series) (2 members)
- Knuckles Clan (1 member)
- Knuckles the Echidna (3 members)
- Line-handling templates (1 member)
- Link modules (1 member)
- List formatting and function templates (3 members)
- Lists (1 member)
- Lists of games (1 member)
- Lizards (1 member)
- Lua-based templates (28 members)
- Lua metamodules (1 member)
- Lua templates with errors (2 members)
- Main page templates (1 member)
- Males (14 members)
- Manga (1 member)
- Mario & Sonic at the London 2012 Olympic Games (1 member)
- Mario & Sonic at the Olympic Games (2 members)
- Mario & Sonic at the Olympic Games Tokyo 2020 (2 members)
- Mario & Sonic at the Olympic Winter Games (2 members)
- Mario & Sonic at the Rio 2016 Olympic Games (2 members)
- Material from Wikipedia (7 members)
- Mathematical formatting templates (1 member)
- Mbox and messagebox templates (2 members)
- Merge templates (1 member)
- Metal Fighters (1 member)