Abstract: Recently, a flurry of activities have been carried out on the isotopic effects in JT-60U, JET and DIII-D, which have shown a favorable confinement trend for heavier hydrogen isotopes. The consensus from these experimental observations was that this is an unsolved puzzle in tokamak plasmas. This is in fact not quite accurate. When the favorable effects were first observed in the 1990s on TFTR for hydrogen, deuterium and tritium experiments, a theoretical attempt was indeed made to understand the results by Lee and Santoro. Apparently, this paper has not attracted much attention in the community. Recently, a paper by Lee and White on the H-mode physics has also described the isotope effects at the H-mode pedestal. In this talk, the theoretical interpretations on these isotopic effects based on 1) the resonance broadening theory in the core as well as 2) the force balance equation for the pedestal from the gyrokinetic theory will be described. The implementation of the related physics in an initial value code such as GTC and/or GTS will also be discussed.