An LA file is an archive used by Libtool, a generic library support script used for creating portable compiled libraries. It contains a library description that may include a reference to a shared or dynamic library. LA files are primarily used to remember the destination directory for the library and the dependency on the math library.

Libtool was designed for building shared libraries on Unix. It uses the LA file to link libraries since static libraries are only archives that contain no metadata in regards to linking other libraries with them. The LA file is the only file used by Libtool for preserving library dependencies, file names, and library versions and revisions between different platforms.