| File extension Name |
extension description |
| .Y | Amiga Yabba Compressed Archive (Amiga) |
| .Y | Xcode Core Yacc Program (Apple Inc.) |
| .Y | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .y | UNIX yacc or bison Parser Generator File |
| .Y | Yabba Compressed File |
| .Y | Desktop Color Separation Specification Yellow Layer |
| .Y | Yacc: Yet Another Compiler-Compiler Grammar File |
| .Y01 | Paradox Secondary Index |
| .Y02 | Paradox Secondary Index |
| .Y03 | Paradox Secondary Index |
| .Y04 | Paradox Secondary Index |
| .Y05 | Paradox Secondary Index |
| .Y06 | Paradox Secondary Index |
| .Y07 | Paradox Secondary Index |
| .Y08 | Paradox Secondary Index |
| .Y09 | Paradox Secondary Index |
| .Y2 | Plugh! |
| .Y64 | Commandos 2 Game Mission |
| .YAB | Yabasic Source |
| .YAL | Arts & Letters Clipart |
| .YANK | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YAP | Castles & Catapults Game File (Infogrames Entertainment SA) |
| .YAR | YAR Archive |
| .YAR | Castles & Catapults Game File (Infogrames Entertainment SA) |
| .YBAK | MindGenius Computer Aided Thinking File Backup (Gael Ltd.) |
| .YBHTM | yBook HTML File (Spacejock Software) |
| .YBK | Encarta Yearbook (Microsoft Corporation) |
| .YBM | Face Bitmap |
| .YBS | YBS Compressed Archive |
| .YBTXT | yBook Text File (Spacejock Software) |
| .YC | YAC Compressed Archive |
| .YCT | YahELite Chat Transcript (David J. Binette) |
| .YDC | Yu-Gi-Oh! Power of Chaos Card Deck (Konami Group) |
| .YDK | Yusuf Data Recovery |
| .YDL | YAODL 3D Scene Description (Silicon Graphics, Inc.) |
| .YDO | Yarston Text Editor Text Document (YARSTON) |
| .YEAH | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YEAR | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YEL | Yellow Color Separation (Adobe Systems Incorporated) |
| .YENC | yEnc Encoded File |
| .YG0 | Paradox Secondary Index |
| .YG1 | Paradox Secondary Index |
| .YG2 | Paradox Secondary Index |
| .YG3 | Paradox Secondary Index |
| .YG4 | Paradox Secondary Index |
| .YGD | Yougoodai Playlist (mode2) |
| .YGF | yEd Graph Editor Y Graph Format (yWorks) |
| .YGM | YahooGroupManager Ver. 1.x Database (GGNetworks) |
| .YGM2 | YahooGroupManager Ver. 2.x Database (GGNetworks) |
| .YGN | yGen Project File (Spacejock Software) |
| .YGO | Paradox Database-related File |
| .YHF | Your Honey Frame Shape File (HotBounce programming & development) |
| .YIF | Mungyodance Game Data (VULPvibe) |
| .YIF | Graphic |
| .YINS | Castles & Catapults Game File (Infogrames Entertainment SA) |
| .YKEY | Castles & Catapults Game File (Infogrames Entertainment SA) |
| .YLD | SMS Yield Monitor Data File (Ag Leader Technology, Inc.) |
| .YLT | TheWord & Bible Companion Young's Literal Translation Bible |
| .YM | Atari ST YM2149 Module/Song (Atari) |
| .YMA | YMAG Center Data Exchange File (Ymag) |
| .YMACRO | YaHoE File |
| .YMAP | MindGenius Computer Aided Thinking File (Gael Ltd.) |
| .YMG | Yahoo! Instant Messenger (Yahoo!) |
| .YML | Sailfish Yacht Analyzer XML-based Data File (Techsail) |
| .YML | Ruby on Rails Database Configuration File (Ruby on Rails Project) |
| .YMP | MicroSim PCBoard Mapping File |
| .YMP | openSUSE One Click Install Metapackage (Novell, Inc.) |
| .YMY | Castles & Catapults Game File (Infogrames Entertainment SA) |
| .YN | Audio Utility Tuningwrench Compressed File |
| .YNC | yEnc Encoded File |
| .YNX | Seqmax Seqprest Compressed Audio File |
| .YORK | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YOU | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YOUD | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YPCL | Castles & Catapults Game File (Infogrames Entertainment SA) |
| .YPF | YahELite Configuration (David J. Binette) |
| .YPK | MicroSim PCBoard Mapping File |
| .YPL | Yahoo! Player Playlist |
| .YPS | Yahoo! Instant Messenger (Yahoo!) |
| .YPT | Cryptic File |
| .YRM | Command & Conquer Yuri's Revenge Unofficial Multiplayer Map (Westwood Studios) |
| .YRO | Command & Conquer Yuri's Revenge Official Multiplayer Map (Westwood Studios) |
| .YSE | Yamaha Studio Editor Session File (Yamaha Corporation) |
| .YSM | Yamaha Studio Manager Session File (Yamaha Corporation) |
| .YSP | Bitmap Graphic |
| .YTR | I.R.I.S. OCR Data (I.R.I.S. s.a.) |
| .YUV | Color Space Pixel Format |
| .YUV3 | CCIR 601 2:1:1 Bitmap |
| .YV | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YV2 | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YWEMANIFEST | Yahoo! Widget Manifest File (Yahoo! Inc.) |
| .YWP | yWriter Project (Spacejock Software) |
| .YYC | Wave Sapphire Distribution File |
| .YZ | Unknown Apple II File (found on Golden Orchard Apple II CD Rom) |
| .YZ | YAC Compressed Archive |
| .YZ1 | DeepFreezer Compressed Archive (BinaryTechnology) |