This matter deals with the effects of the ionizing radiation. It begins with the study of the atomic nucleus to continue with the radioactive decay and the ionizing electromagnetic radiations. The energetic production from the nuclear reactors is assessed in simplified form, as well as the possible risks that can be produced in this process. The treatment of the generated waste is also studied. Later, the different mechanisms of interaction of radiation with matter along with principal concepts of dosimetry are described. This leads us to the study of the principal biological effects. Finally, in the las chapter, the problem of the radiactive waste management (transport, storage...) is addressed.