| B | Lotus Applause Batch List | 
| B&W | Atari, Macintosh Bitmap Picture | 
| B_W | Atari, Macintosh Picture | 
| B1J | BookJones | 
| B1N | 1st Reader Binary Screen Image | 
| B1S | BookSmith | 
| B30 | Ventura Publisher Printer Font | 
| B3D | 3D Builder File | 
| B4 | Helix Nuts and Bolts File | 
| B64 | Base 64 MIME-encoded File | 
| B8 | Piclab Raw Graphic File | 
| BA$ | Microsoft compressed BAS, decompress with UNPACK.EXE | 
| BAC | Backup File | 
| BAD | Rime Mailer Address | 
| BAD | Rime Mailer Address File | 
| BAG | AOL Instant Messenger File | 
| BAG | Archive (Emperor: Battle for Dune) | 
| BAK | Backup File | 
| BAL | Ballade Music Score | 
| BAL | BAL Borland Programming Language Source | 
| BAN | Sierra Print Artist Banner | 
| BAR | dBase Application Generator Horizontal Menu Object | 
| BAR | UNIX Archive | 
| BAS | BASIC Language Source Code | 
| BAT | Batch File | 
| BB | Papyrus Database Backup | 
| BBL | TeX/BibTeX Bibliographic Reference File | 
| BBM | Deluxe Paint Brush Bitmap File | 
| BBS | Bulletin Board System Text | 
| BC | Sierra Print Artist Business Card | 
| BCF | 3D Body Mesh File (The Sims) | 
| BCH | dBase Application Generator Batch Process Object | 
| BCH | Phoenix Software (Datalex) Entry Point 90 Data File | 
| BCK | Backup | 
| BCM | MS Works Communications File | 
| BCO | Bitstream Fontware File | 
| BCP | Borland C++ Makefile | 
| BCW | Borland C++ 4.5 Environment Settings | 
| BDB | MS Works Database Backup | 
| BDE | Borland Database Engine  (various) | 
| BDF | West Point Bridge Designer File | 
| BDF | Adobe Bitmap Distribution Format font | 
| BDR | Microsoft Office 97 or Publisher Document Border | 
| BEZ | Bitstream Fontware File | 
| BF2 | Bradford 2 Font | 
| BFA | Blowfish-encrypted File (Extension added to original) | 
| BFC | Briefcase File | 
| BFL | Colin McRae Rally 2 Data File | 
| BFM | Jane's Combat Simulations F-15 | 
| BFX | BitFax Document | 
| BG | Backgammon for Windows Game | 
| BGA | OS/2 Graphic Array | 
| BGB           | MS Chat Background Graphic | 
| BGI | Borland Graphic Interface | 
 | BGL | Flight Simulator Scenery File | 
 | BHF | pcAnywhere Host File | 
| BHX | Archive |