This review presents data on the influence of $\gamma$-irradiation (10$^{11}$--10$^{12}$ kW/cm$^2$) on the process of crystallization of metals and alloys. Studies are presented of the structure, phase composition, crystallization parameters, and redistribution of impurities along single crystals. We show that the relationship between the phase and structural components changes under irradiation, while an improvement of the structure of single crystals of metals and alloys, an enhancement of the efficiency of purifying them of impurities, more intensive mixing of alloys, and a decrease in the thickness of the diffusion layer at the melt-crystal phase boundary take place. Under the action of $\gamma$-irradiation the crystallization parameters are altered: the equilibrium temperatures of the process and the segregation coefficients of impurities. This alters the crystallization mechanism. Possible mechanisms of the observed phenomena are discussed.