Isotope effect may refer to: Equilibrium isotope effect, see Equilibrium constant#Effect of isotopic substitution Isotopic shift, effect of isotopic substitution on spectroscopy Kinetic isotope effect, effect of isotopic substitution on chemical reaction rates Magnetic isotope effect, when a chemical reaction involves spin-selective processes, such as the radical pair mechanism Superconductive transition temperature varying by isotope atomic weight: see BCS theory#Underlying evidence