The DESCRIPTOR SYSTEMS Toolbox for MATLAB [1] is partly based on the RASP-DESCRIPT routines implemented in Fortran 77 and partly based on the free control software library SLICOT. The underlying algorithms are among the most complex procedures ever employed in the control field and encompass computations like the determination of complete Kronecker structure of linear pencils, generalized pole assignment and stabilization, model conversions (descriptor state-space to rational/polynomial representations), general rational factorisations (inner-outer, normalized coprime), generalized inverses (left/right, week, Moore-Penrose), etc. This package illustrates the new trend in CACSD to employ high quality, robust control software written in high level langages (e.g., Fortran) in user-friendly environments like MATLAB via appropriate gateways (mex-files).