| i3 | Modula-3 Interface Source Code |
| ian | COOL:Jex Business Team Model |
| iap | Infinity Engine Add-on Patcher File |
| ib | Embarcadero InterBase Database File |
| ibplugin | Interface Builder Plug-in |
| ib_mon | IncrediBuild Build Progress Data |
| ic | Esterel Intermediate Code |
| icf | Implementation Configuration File |
| icfg | Aristotle Interprocedural Control Flow Graph |
| ici | ICI Source Code |
| icp | Remote Call Profiler Data |
| icu | ICU Data |
| icz | Lib2Def Output File |
| id0 | IDA Database |
| id1 | IDA Database |
| ida | Internet Data Administration Script |
| idapi | Borland Database Engine IDAPI Data |
| identcache | RAD Studio Refactoring Data |
| idh | OpenCBM File |
| idk | Interface Development Kit Archive |
| idl | Interface Definition File |
| idle | IDle Script Source |
| idll | CodeWarrior DLL |
| idml | Adobe InDesign Markup Language Document |
| idn | Alpha Five Index Definition File |
| idol | IDle Object Library |
| idt | Windows Installer Exported Database |
| idy | Micro Focus COBOL Debug Data |
| iex | Elixir Interactive Shell Script |
| ifm | IBM WebSphere Interface Mapping |
| ifm | FactoryTalk View Studio Information Message Component File |
| ifr | UEFI IFR Opcode |
| ih | C++ Internal Header |
| ihex | Intel HEX Format Data |
| ihp | Watcom C Compiler Help |