The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Biology (6 members)
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- Biophilia (1 member)
- Biotech (13 members)
- Biotico (5 members)
- Birds (16 members)
- Bittersweet (33 members)
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- BoneDiagrams (39 members)
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- Book (1 member)
- Books (488 members)
- Bootcamp Caminos de Siembra (2023) (26 members)
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- Bowfishing (1 member)
- Brazil (22 members)
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- Brighton (3 members)
- Bristol (12 members)
- Bristol files (3 members)
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- British Columbia (7 members)
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- Building elements (33 members)
- Building materials (1 member)
- Building with Pumice (13 members)
- Buildings (12 members)
- Built environment (127 members)
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- Business (52 members)
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- CAD (2 members)
- CAN handbook (66 members)
- CASWiki topic news by place (1 member)
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- CASwiki resources by place (8 members)
- CASwiki stubs (62 members)
- CASwiki topic news (131 members)
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- CC-BY-2.0 files (3 members)
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- Capstone (1 member)
- Carbon footprint (8 members)
- Cardiovascular diseases (1 member)
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- Caribbean Climate Adaptation Strategies Through Sustainability (2 members)
- Cartografías Líquidas (62 members)
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- Catholic Relief Services (64 members)
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- Chemical substances (8 members)
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- Chriswaterguy's CCS notes (3 members)
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- Cities (57 members)
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- Civics maps (19 members)
- Clarion University of Pennsylvania (8 members)
- Classroom activities (2 members)
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- Clay Brick and Tile Moulding Equipment (17 members)
- Clean water (11 members)
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- Climate (2 members)
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- Climate change (198 members)
- Clinical safety (1 member)
- Clothes (2 members)
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- Coffee (11 members)
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- Collapse (1 member)
- Colombia (13 members)
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- Colostomy in Newborns (8 members)
- Comas (6 members)
- Combustion (2 members)
- Commerce (4 members)
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- Comparisons (7 members)
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- Composting (155 members)
- Composting toilets (21 members)
- Computer (2 members)
- Computer-aided design (13 members)
- Computer based education (0 members)
- Computer vision (28 members)
- Computers (8 members)
- Comunidad El Majahual (4 members)
- Comunidad El Zonte (5 members)
- Comunidad SUPRA (124 members)
- Comunidad Supra (1 member)
- Concrete (24 members)
- Concrete Block Producing Equipment (19 members)
- Conferences (7 members)
- Conservation (19 members)
- Constructed wetlands (22 members)
- Construction (307 members)
- Construction and Materials (2 members)
- Construction and materials (133 members)
- Construction and materials videos (51 members)
- Content (0 members)
- Content by location (20 members)
- Content by topic (17 members)
- Content by type (16 members)
- Content management systems (1 member)