E. Roanes-Macias and E. Roanes-Lozano* (Spain), eroanes@eucmos.sim.ucm.es About how to implement Geometric Transformations on a CAS The purpose of this paper is to give the basic ideas about how to elaborate an implementation on a CAS of the transformations in the 3-dimensional real Euclidean space. These transformations could be defined in three optional ways: in synthetic mode, by its equations, or by taking a given list of points into another one. We also describe how to classify the product transformations, find fixed planes, split isometries as product of reflections and obtain a plot of a polygonal line and its image. Some practical and didactic comments are included. We also describe our implementation in Maple V.