[en] The effects of an irradiation on metals or alloys are briefly described along the two lines of instantaneous processes (fundamental aspects) and of structural evolution (practical applications). Irradiation creates defects in metals, but also anneals them out; induces hardening, but also softening; introduces disorder, b.a. order... We shall hereunder describe-and in some cases explain - some of these b.a.'s. We shall, in a first part, recall briefly the instantaneous processes taking place in a metal under flux. A second part will be devoted to the evolution of the metal being irradiated. Obviously, this first section will have a more or less low temperature fundamental character, the second one considering rather the high temperature experiments, with a definite technological flavour