An introduction and elementary treatment of mass transfer is presented here. The conditions for similarity of concentration and velocity profiles, and temperature and concentration profiles have been discussed and the relevant dimensionless numbers have been defined. Stefan law has been presented in Sect. 15.4, which can be utilized for experimental determination of the diffusion coefficient. Convective mass transfer has been discussed and dimensional analysis has been used to determine functional relations for free and forced flow conditions, which is followed by presentation of mass transfer correlations. In Sect. 15.8, analogies for convection heat transfer have been extended to the mass transfer problems.