GILDAS is a collection of software oriented toward (sub-)millimeter radioastronomical applications (either single-dish or interferometer). It has been adopted as the IRAM standard data reduction package and is jointly maintained by IRAM & CNRS. GILDAS contains many facilities, most of which are oriented towards spectral line mapping and many kinds of 3-dimensional data. The code, written in Fortran-90 with a few parts in C/C++ (mainly keyboard interaction, plotting, widgets), is easily extensible.