Special attention in the monograph is given to the effect of the type and concentration of impurity and alloying elements, and also phase changes on the mechanisms of buildup of radiation defects and damage to metallic materials under radiation. The accurate description of these processes is based on the considerations regarding the interaction of radiation point defects with each other and dissolved elements, the diffusion of point defects and dissolved elements, radiation-enhanced diffusion and phase transformations in irradiation. Detailed analysis of the radiation damage and methods of suppressing of this type of damage on the basis of taking into account the real structure, chemical and phase composition of metals and alloys has become possible as a result of advances in a number of fundamental area as of radiation physics of solids: theory of defects in alloys, low-temperature kinetics of buildup and annealing of radiation defects in diluted and concentrated solid solutions, radiation-enhanced diffusion, phase instability. The most important results in this area include the development of concepts of the interaction of interstitial atoms with the atoms of dissolved elements, their diffusibility, and the mechanism of migration in diluted and concentrated solid solutions, the diffusion transfer of dissolved elements and interaction with sinks. An important section of the book is concerned with the calculations and experimental evaluation of the activation parameters of individual chemical elements and alloys, and a number of methods of reducing the activation of materials is examined. General directions and problems of development of reduced-activation radiation-resistant alloys are analysed. The final chapter deals with the main experimental relationships and mechanisms of radiation damage in a number of pure metals and constructional materials for atomic and thermonuclear engineering, determined by the processes of radiation hardening, embrittlement, creep and swelling.