The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- A People's Food Policy (43 members)
- A People’s Food Policy (0 members)
- Aalto University (51 members)
- About Appropedia (0 members)
- Abstracts on Sustainable Agriculture (15 members)
- Academia (8 members)
- Accessibility (12 members)
- Activism (24 members)
- Activist pages (3 members)
- Acute Appendicitis (6 members)
- Adaptación al cambio climático (1 member)
- Additive manufacturing (5 members)
- Adelaide (3 members)
- Adelaide files (1 member)
- Adelaide images (0 members)
- Aerosol pandemic (32 members)
- Africa (104 members)
- Africa files (29 members)
- Africa images (0 members)
- African American Environmentalist Association (17 members)
- Agricultural subsidies (1 member)
- Agriculture (601 members)
- Agriculture manual (21 members)
- Agrivoltaic (1 member)
- Agrivoltaics (37 members)
- Agroforestry (9 members)
- Agua y Suelo para la Agricultura (ASA) (58 members)
- Aid (11 members)
- Aid and development workers (21 members)
- Air Quality (1 member)
- Air conditioning (16 members)
- Air pollution (35 members)
- Air purification (1 member)
- Air quality (18 members)
- Air travel (4 members)
- Akvo ATOC (10 members)
- Akvopedia (1 member)
- Alcohol fuels (18 members)
- Algae (5 members)
- Alternative building (119 members)
- Alternative building design (3 members)
- Alternative energy (1 member)
- Alternative propulsion (3 members)
- Amaranth (12 members)
- Ambiental (8 members)
- America files (33 members)
- America images (0 members)
- AmoSmile (61 members)
- Amsterdam (1 member)
- Anaerobic digestion (32 members)