| hkk | HTML Help AutoIndex |
| hks | HTML-Kit Script |
| hla | High Level Assembly Source Code |
| hlsl | Microsoft DirectX D3D High Level Shader Language |
| hm | WinHelp Context ID |
| hoc | HOC Script |
| hpack | Haskell Package |
| hpf | High Performance Fortran Source Code |
| hpp | C++ Header File |
| hpw | CompuServe Home Page Wizard Document |
| hql | Apache Hive HiveQL Script |
| hrl | Erlang Header File |
| hs | Haskell Source |
| hsdl | Hierarchical Scan Description Language Data |
| hse | Homesite Snippet End |
| hsm | Assembly Header File |
| hsp | WinDev HyperFileSQL Stored Procedure |
| hss | Homesite Snippet Start |
| htl | HTL Source |
| htp | htp Source File |
| hx | Haxe Source Code |
| hxa | MS Help 2 Project Attribute Definition |
| hxc | MS Help 2 Project Collection Definition |
| hxe | MS Help 2 Project Sample Definition |
| hxf | MS Help 2 Project Include File |
| hxk | MS Help 2 Project Index |
| hxml | Haxe Compiler Options |
| hxt | MS Help 2 Project ToC |
| hxv | MS Help 2 Project Virtual Topic Definition |
| hxx | C++ Header File |
| hydra | Hydra Image Filter Program |
| hzx | CrossWorks for ARM Linked Executable |
| i | Visual C++ Preprocessed Source |
| i | INTERCAL Source File |
| i3 | Modula-3 Interface Source Code |