The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Isaac Asimov (3 members)
- Isaac Babel (1 member)
- J. G. Ballard (2 members)
- J. R. R. Tolkien (2 members)
- Jack London (2 members)
- Jack McDevitt (0 members)
- James Baldwin (10 members)
- James Joyce (2 members)
- James Tiptree Jr. (1 member)
- Jeff VanderMeer (1 member)
- Jo Ann Beard (1 member)
- Johann Wolfgang von Goethe (2 members)
- John Donne (3 members)
- John Dryden (0 members)
- John Keats (6 members)
- Jorge Luis Borges (2 members)
- Journal (29 members)
- Journal Templates (39 members)
- Juan Rulfo (1 member)
- Judith Ortiz Cofer (1 member)
- Julio Cortázar (1 member)
- Jupiter-3 1.5/50 (22 members)
- Jupiter-8 2/50 (34 members)
- Jupiter-9 2/85 (11 members)
- Karl Marx (1 member)
- Kate Chopin (2 members)
- Kazuo Ishiguro (1 member)
- Ken Kesey (1 member)
- Kim Stanley Robinson (2 members)
- Kiron 2/28 (10 members)
- Kodak Ektar 100 (9 members)
- Kodak Portra 400 (57 members)
- Kodak ProImage 100 (4 members)
- Kurt Vonnegut (4 members)
- LIT 3101 (1 member)
- Landscape (4 members)
- Landscapes (429 members)
- Langston Hughes (1 member)
- Led Zeppelin (1 member)
- Leica (149 members)
- Leica M (1 member)
- Leica M8 (94 members)
- Leica SL (52 members)
- Leica SL 📷 (1 member)
- Leica m8 (2 members)
- Lenses (101 members)
- Leo Tolstoy (1 member)
- Leslie Marmon Silko (1 member)
- Life (135 members)
- Linux (21 members)