Book excerpt: Intrinsic point defects due to high energy particle irradiation are studied in terms of anelastic principles and experimental techniques. A critical assessment of available data on binding and diffusion energies of self-interstitials and self-interstitial solute atom complexes is given. New results are presented for the elastic aftereffect of self-interstitials and caging motions, i.e., localized diffusion of metallic interstitial atoms. A novel point discussed is how the design of torsion pendulum and vibrating reed devices are affected by in situ irradiations with electrons. The dynamics of elastic dipoles are outlined and supplemented by the results of computer simulations.