| 1 | Y | Stephen C. Johnson | Yacc Source Format |
| 2 | Y01 | Corel Corporation | Corel Paradox Secondary Index |
| 3 | Y02 | Corel Corporation | Corel Paradox Secondary Index |
| 4 | Y03 | Corel Corporation | Corel Paradox Secondary Index |
| 5 | Y04 | Corel Corporation | Corel Paradox Secondary Index |
|
| 6 | Y05 | Corel Corporation | Corel Paradox Secondary Index |
| 7 | Y06 | Corel Corporation | Corel Paradox Secondary Index |
| 8 | Y07 | Corel Corporation | Corel Paradox Secondary Index |
| 9 | Y08 | Corel Corporation | Corel Paradox Secondary Index |
| 10 | Y09 | Corel Corporation | Corel Paradox Secondary Index |
| 11 | YAB | Yabasic | Yabasic Source Code |
| 12 | YAJL | lloyd | YAJL Script |
| 13 | YAML | N/A | YAML Document |
| 14 | YBHTM | Spacejock Software | YBook HTML |
| 15 | YCT | David Binette | YahELite Chat Transcript |
| 16 | YEL | N/A | Yellow Color Separation |
| 17 | YENC | N/A | YEnc Format |
| 18 | YG0 | Corel Corporation | Corel Paradox Secondary Index |
| 19 | YG1 | Corel Corporation | Corel Paradox Secondary Index |
| 20 | YG2 | Corel Corporation | Corel Paradox Secondary Index |
| 21 | YG3 | Corel Corporation | Corel Paradox Secondary Index |
| 22 | YG4 | Corel Corporation | Corel Paradox Secondary Index |
| 23 | YM | Atari | Atari ST Audio Format |
| 24 | YML | N/A | YAML Document |
| 25 | YNC | N/A | YEnc Encoded Format |
| 26 | YTD | Rockstar Games | Grand Theft Auto 5 Texture File |
| 27 | YUV | N/A | YUV Encoded Image Format |
| 28 | YWL | Repkasoft | YoWindow Data |
| 29 | YXX | N/A | Bison source code |
| 30 | YZ1 | Yamazaki ZIPPER | Yamazaki ZIPPER Format |
