The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- 3rd Rock Wiki (1 member)
- 3rd Rock from the Sun (1 member)
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- Albright Family (1 member)
- Aliens (13 members)
- Article management templates (4 members)
- Article stubs (0 members)
- Aubrey Pitman (1 member)
- Blog posts (2 members)
- Browse (6 members)
- Candidates for deletion (0 members)
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- Cast (15 members)
- Catchphrases (12 members)
- Category templates (4 members)
- Characters (34 members)
- Citations needed (0 members)
- Cities (1 member)
- Community (4 members)
- Content (3 members)
- Copyright (1 member)
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- Crew (9 members)
- DVDs (7 members)
- Directors (1 member)
- Disambiguations (0 members)
- Episodes (140 members)
- Female (1 member)
- Female Cast (5 members)
- Female Characters (7 members)
- Finales (6 members)
- Forum (2 members)
- Forums (7 members)
- General wiki templates (34 members)
- Guest Characters (1 member)
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- Help (4 members)
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- Main Characters (6 members)