While isotope effects are, by the Bigeleisen equation, understood as the result of changes in force constants involving the isotopic atom, a plethora of observed isotope effects result from processes that apparently do not introduce such changes. These include secondary kinetic isotope effects, as well as isotope effects on chromatographic retention times, vapor pressure isotope effects, isotope effects on diffusion, miscibility of liquids, and many other physical processes. They are important from the practical point of view as they are used in the technological processes of isotopic enrichment that finds their place in the newest applications in nanomaterials. In this presentation, we ll provide several examples and address the origins of these phenomena from the computational point of view.