[en] This paper analyzes the evolution of the most relevant aspects of safety and environmental protection as fundamental elements of the development of nuclear energy in the international framework. The stages leading to the preventive approach to safety in the fifties and in the sixties are also highlighted. During these years, the 'defence in depth' principle was established as the basis for the consequent evolution of the nuclear safety regulations. In this context accident prevention was entrusted to a highly reliable set of redundant systems that could be passive or actuated in a manual or automatic way. In the 1970's, following the accidents of Browns Ferry and Three Mile Island nuclear power plants, an impulse was given to the systematic safety assessment and to the trend of the so-called Probabilistic Risk Assessment (PRA). The paper takes into account the aspects of risk perception as the social effect of Three Mile Island and Chernobyl accidents. This subject has led both to public awareness about the chronic and traumatic risk deriving from a severe accident and, in the international framework, to a process of plants design optimization towards safety and environmental protection. The general aspects of safety and environmental protection are then completed by an overview of the regulatory policies, with particular reference to the licensing procedures developed in Italy