| T | Tape archive (TAR) (Without compression) |
| T2T | Modeling software file (Sonata CAD) |
| T44 | Temporary file for sorting index (dBase IV) |
| T64 | Emulator tape image file (Commodore 64) |
| TAB | Guitar Tablature file |
| TAG | Query tag name file (DataFlex) |
| TAH | Turbo assembler help file (Borland C++) |
| TAK | Tom's lossless Audio Kompressor (TAK) audio compression file |
| TAL | Text illustration file (TypeAlign) |
| TAR | Compressed archive (TAR) |
| TAZ | Compressed ASCII archive (TAR) |
| TB1 | Font file (Borland Turbo C) |
| TB2 | Font file (Borland Turbo C) |
| TBF | Fax document (Imavox TurboFax) |
| TBK | Memo backup file (dBase IV) |
| TBL | Table of values (OS/2) |
| TBO | Turbo Architecture Database (used by U.S. Federal Highway Administration's "Turbo Architecture" program) |
| TBS | Text elements (Microsoft Word for Windows) |
| TBX | Table (Project Scheduler 4) |
| TC | Configuration file (Borland C++) |
| TCF | Test Crafter File (storage file for tests developed in Cambridge UP software) |
| TCH | Turbo C Help file (Borland C++) |
| TCL | Script in the TCL/TK Language |
| TCW | Drawing file (TurboCAD for Windows) |
| TD | Configuration file (Turbo Debugger for DOS) |
| TD0 | Disk image file (Teledisk) |
| TD2 | Configuration file (Turbo Debugger for WIN32) |
| TD4 | Saved track design (Roller Coaster Tycoon) |
| TDB | Database file (TACT) |
| TDF | Typeface definition file (Speedo) |
| TDH | Help file (Turbo Debugger0 |
| TDK | Keystroke recording file (Turbo Debugger) |
| TDS | Symbol table (Turbo Debugger) |
| TDW | Configuration file (Turbo Debugger for Windows) |
| TEF | Fax document (Relisys TEFAX) |
| TEL | Hostfile (Telnet) |
| TEM | Input template (IconAuthor) |
| TEX | TEX text file (Scientific Word) |
| TF | Configuration file (Turbo Profiler) |
| TFA | Area file (Turbo Profiler) |
| TFC | Catalogue file (Tobi's Floppy Disk Cataloguer) |
| TFH | Help file (Turbo Profiler) |
| TFM | TeX font metrics file (TeX) |
| TFS | Statistics file (Turbo Profiler) |
| TFW | ArcView World file for TIF image (GIS application) |
| TG1 | Project file (On Target) |
| TGA | Targa bitmap (Countour Mortgage Loan Format) |
| TGL | Totally Games Localization file used in gaming software. |
| TGQ | Movie file (Dungeon Keeper 2) (Bullfrog Software) |
| TGV | Video file (Electronic Arts) (Need for Speed I/II/III, NBA '96) |
| TGZ | Gzip/Tape archive (Unix) |
| THAI | Husquvania sewing machine file |
| THEME | Desktop theme (Microsoft Windows 9.x) |
| THM | Thumbnail image file (Microsoft Clip Gallery v.1.x) |
| THN | Thumbnail (Graphics Workshop for Windows) |
| THS | Thesaurus dictionary (WordPerfect for Windows) |
| TIB | Disk imaging file for Acronis True Image backup and recovery program. |
| TIF | Tag image bitmap file (TIFF) |
| TIFF | Tag image bitmap file (TIFF) |
| TIG | Map file (Tiger) (Used by the US Government to distribute Map files) |
| TIL | Fuzzy Logic knowledge base file (Togai InfraLogic Fuzzy-C Compiler) |
| TIM | Texture/Image file (Playstation) |
| TIS | Tile set (MahJongg 3.0) |
| TJF | backup files (VAXTPU Editor) |
| TLB | Reference table (Bubble Editor) |
| TLC | Compiled tool command language source code file (Swat) |
| TLE | Two-Line element set (NASA) |
| TLP | Project timeline file (Microsoft Project) |
| TLX | Data file (Trellix) |
| TMD | TextMaker document from SoftMaker |
| TMF | Tagged font metric file (WordPerfect for Windows) |
| TMO | Ztg global optimizer default optimizer file (Zortech C++) |
| TMP | Temporary file (Microsoft Windows) (ALL) |
| TMS | Script file (Telemate) |
| TNV | Data file (BitWare) |
| TOC | Table of contents file (Eudora Mailbox) |
| TOC | Adobe FrameMaker table of contents file |
| TOL | Image file (Kodak Photo Enhancer) |
| TORRENT | BitTorrent file |
| TOS | Self-Extracting archive (Atari ST) |
| TP | Sesson-state file (Turbo Profiler) |
| TP3 | Template file (Harvard Graphics) |
| TP4 | Saved picture file (Roller Coaster Tycoon) |
| TPB | Downloadable PCL Soft font file backup (HiJaak) |
| TPF | Downloadable PCL Soft font file (HiJaak) |
| TPH | Help file (Turbo Pascal) |
| TPL | Template file (Harvard Graphics, Microsoft Access, Cakewalk Audio and others) |
| TPP | Protected mode units (Borland Pascal 7.0) |
| TPU | Command file (VAXTPU Editor) |
| TPV | Packed graphics file (TutorPro) |
| TPW | Packed wave files (TutorPro) |
| TPX | Image file (ULead Photo Express) |
| TPZ | Compressed archive (GNUzip) |
| TR | Session-state settings (Turbo Charge Debugger for DOS) |
| TR2 | Session-state settings (Turbo Charge Debugger for Win32) |
| TRA | Saved game file (Coaster) |
| TRC | Debug support file (Power CTrace) |
| TRE | Directory tree file (PC-Tools) |
| TRIF | Tiled Raster Interchange Format |
| TRK | Script file (Kermit) |
| TRM | Terminal settings file (Microsoft Windows 3.x) |
| TRN | Project usage log (MKS Source Integrity) |
| TRS | Executable file (MicroGraphix) |
| TRW | Session-state settings (Turbo Debugger for Windows) |
| TS | HDTV sample file (Transport Stream MPEG-2 video stream) |
| TSH | Broderbund Creatacard Transfer Project |
| TSK | Compaq iPaq picture image |
| TST | Printer test file (WordPerfect for Windows) |
| TSV | Tab-separated values file |
| TTF | TrueType font (Generic) |
| TTK | Translation tool kit file (Corel Catalyst) |
| TTO | Client access data specification file (AS/400) (Server to Client) |
| TUB | Corel Paint Shop Pro Tube File |
| TUV | Tutorial file (Many programs use this suffix for their tutorials) (Generic) |
| TV | Table view settings (Paradox) |
| TV1 | Overflow file above insert point in document 1 (WordPerfect for Windows) |
| TV2 | Overflow file above insert point in document 2 (WordPerfect for Windows) |
| TV3 | Overflow file above insert point in document 3 (WordPerfect for Windows) |
| TV4 | Overflow file above insert point in document 4 (WordPerfect for Windows) |
| TV5 | Overflow file above insert point in document 5 (WordPerfect for Windows) |
| TV6 | Overflow file above insert point in document 6 (WordPerfect for Windows) |
| TV7 | Overflow file above insert point in document 7 (WordPerfect for Windows) |
| TV8 | Overflow file above insert point in document 8 (WordPerfect for Windows) |
| TV9 | Overflow file above insert point in document 9 (WordPerfect for Windows) |
| TVF | Table view settings (dBase IV) |
| TWD | MindMapper Brainstorm and Visual Map file |
| TWF | Data file (TABWorks) |
| TWW | Template file (TagWrite) |
| TX8 | MS-DOS text |
| TXB | Encoded briefing file (Descent/D2) |
| TXF | Compressed archive (FREEZE) |
| TXI | Support file (TeX) |
| TXW | Wave file (Yamaha TX16W) |
| TYM | Time Stamp files (PageMaker 4.0) |
| TZ | Old compression file (TAR), (COMPRESS) |
| TZB | Compressed archive (Tar) |
