This work presents an overview of the most important mechanisms of radiation damage in silicon detectors to be used for high energy experiments in LHC. The changes in the shallow concentration have been studied by thermally stimulated currents (TSC) after proton and neutron irradiation with fluences up to 10/sup 15/ cm/sup -2/ to investigate the role of thermal donors and the donor-removal effect in standard and oxygen enriched silicon with different resistivities. Deep defects in irradiated silicon have been analysed by deep level transient spectroscopy (DLTS) and photo induced current transient spectroscopy (PICTS) in the same materials. The radiation-induced microscopic disorder has been related with the carrier transport properties of irradiated silicon measured by the Hall effect, by capacitance and current vs. voltage characteristics and with charge collection efficiency. The dependence of the irradiated silicon detectors performances on crystal orientation, on incident particle type and on the initial concentration of oxygen and carbon is also discussed.