The knowledge of diffusion is crucial in many processes because reactions and separations are often limited by a diffusional process.Different approaches to describing diffusion transfer are presented

and the existing models for estimation of the diffusion coefficients in non-electrolytic solutions are discussed in this paper.The most widely applied models are combinations of interpolation schemes

with the diffusion coefficients at infinite dilution.The phenomenological approach is capable of modeling variations of diffusion coefficients with molar fraction.Another series of models for the estimation of diffusion coefficients are based on the concepts of free volume and activation energy.However

all the variations of this approach operate in term of self-diffusion coefficients

and the self-diffusion coefficients may be related to mutual diffusivities by mixing rules.The approach of molecular dynamics simulation is developing

and widely used for the estimation of self-diffusion

but the strong influence of fluctuations makes it difficult to estimate the mutual diffusion coefficients with good accuracy in a reasonable time.Finally

the evaluation of diffusion coefficients for multi-component mixtures is also presented

and the future research in this area is proposed.