The two film resistance model for n -component mass transfer across fluid-fluid interfaces is developed. Arguments are presented in favour of the use of the Generalized Maxwell-Stefan (GMS) diffusion coefficients to describe the transport process. The GMS diffusion coefficients are amenable to molecular interpretation and prediction and multicomponent mass transfer coefficients defined in terms of them are shown to possess simple addivity property. The effect of thermodynamic non-idealities on intra- and inter-phase mass transport processes are brought out in the analysis.