This chapter discusses pressure effect for diffusion in solid elements and (homogeneous) binary alloys. Semilogarithmic plot of the self-diffusion coefficient of solid elements like Na, Ge, Pb, P and U is illustrated as a function of pressure. Semilogarithmic plot of diffusion coefficient of As in Si and diffusion coefficient of Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg and Sn in Pb versus reciprocal temperature for various pressures is plotted. Similarly, semilogarithmic plot of the interdiffusion coefficients of Cu-Zn alloy, Al-Zn alloy, Fe-Ni alloy, Fe-V alloy is presented. Semilogarithmic plot of the diffusivity versus pressure at 600 K for Cu, Pd, Au, Ni, Zn, Ag, Cd, Hg and Pb in Pb is illustrated. In addition, the chapter illustrates the plot of activation volume versus temperature for diffusion of various elements in Na, Cu, Au, Zn, Ag, In, Sb, Cd, Al, Fe, Au-Zn alloy, Cu-Zn alloy and Fe-Ni alloy.