The modifications of insulating materials by ion implantation can be of considerable interest for many applications. If ion implantation has considerable potential for changing the properties of insulators, only a few experiments have determined the critical parameters which are important in the behaviour of the implanted layer. As a matter of fact, the ion implantation process is, by its very nature, a non-equilibrium process and, in addition, the injection of charged particles in a lattice determines a concomitant creation of intrinsic lattice defects. These defects are associated with the nuclear part of the energy loss of the particles and sometimes with the electronic one (halide compounds). The characterization of these intrinsic defects and the knowledge of their spatial distribution in the lattice are necessary because the formation or dissolution of phases precipitated in the implanted layer are strongly influenced by point or extended defects.