The GOCAD research program is specially devoted to the Geometric Modelling of complex geological objects in connection with Geophysical, Geological and Reservoir Engineering applications. It is based on a new interpolation technique called “Discrete Smooth Interpolation” (DSI) designed to account for the heterogeneous and imprecise data encountered in geology. The basic principle of the DSI method and the main specifications of the associated GOCAD software are presented in this paper.