LHA or LZH is a freeware compression utility and associated file format. It was created in 1988 by Haruyasu Yoshizaki (吉崎栄泰, Yoshizaki Haruyasu), a doctor and originally named LHarc. A complete rewrite of LHarc, tentatively named LHx, was eventually released as LH. It was then renamed to LHA to avoid conflicting with the then-new MS-DOS 5.0 LH ("load high") command. The original LHA and its Windows port, LHA32, are no longer in development because Yoshizaki is busy at work.

Although no longer much used in the west, LHA remained popular in Japan until the 2000s. It was used by id Software to compress installation files for their earlier games, including Doom and Quake. Because some versions of LHA have been distributed with source code under the permissive license, LHA has been ported to many operating systems and is still the main archiving format used on the Amiga computer, although it competed with LZX in the mid 1990s. This was due to Aminet, the world's largest archive of Amiga-related software and files, standardising on Stefan Boberg's implementation of LHA for the Amiga.

Microsoft released the Microsoft Compressed (LZH) Folder Add-on, which was designed for the Japanese version of Windows XP. The Japanese version of Windows 7 ships with the LZH folder add-on built-in. Users of non-Japanese versions of Windows 7 Enterprise and Ultimate can also install the LZH folder add-on by installing the optional Japanese language pack from Windows Update.