QSopt's callable function library provides a set of functions for creating, manipulating, and solving LP problems. The library is written in the (ANSI) C programming language, and it is distributed as a header file qsopt.h and as an archive file qsopt.a on UNIX/LINUX systems, and as a dynamic link library QSlib.dll on Windows systems. Thread-safe versions of the library are available for use in re-entrant programming applications. A complete list of functions can be found in Callable Libarary Function List. The QSopt Reference Manual is a printable document describing the Callable Function Library. An alpha version of the C library has been ported to Java as well, see Java software.

To make the best use of the library, the user should be familiar with the C programming language; excellent references for C are The C Programming Language, Second Edition, B. W. Kernighan and D. M. Ritchie (Prentice Hall, Englewood Cliffs, 1988) and A C Reference Manual, S. P. Harbison, III and G. L. Steele, Jr. (Prentice Hall, Upper Saddle River, 2002).