It is a set of routines written in ANSI C and organized in the form of a callable library.

GLPK uses the revised simplex method and the primal-dual interior point method for non-integer problems and the branch-and-bound algorithm together with Gomory's mixed integer cuts for (mixed) integer problems.

GLPK was developed by Andrew O. Makhorin (Андрей Олегович Махорин) of the Moscow Aviation Institute.

Since version 4.0, GLPK problems can be modeled using GNU MathProg (GMPL), a subset of the AMPL modeling language used only by GLPK.

However, GLPK is most commonly called from other programming languages.