In this chapter we will first of all discuss the fate of charged particles and γ-quanta travelling through matter with energies which are some orders of magnitude in excess of the mean binding energy of the electron, otherwise called the mean ionization potential Ī, i.e. with energies of 0.01–0.1 MeV and more. Here we should note that electromagnetic interactions play the main role in the transport of charged particles and γ-quanta through matter. We should also note that the influence of nuclear forces is generally insignificant due to their short-range character. It is further recognized in this same context that the number of electrons is generally far greater than the number of nuclei.