The influence of feed-side concentration polarization and the resistance of the porous support on membrane processes where solution-diffusion-type composite membranes are involved is discussed in this paper. Reverse osmosis, nanofiltration, gas permeation, prevaporation and vapor permeation represent the complete variation of liquid and gaseous state at the feed and permeat side and cover cases where the driving force is realized by increasing the feed-side potential and cases where the permeate-side potential is decreased. In the calculations, the major parameters, especially feed-side concentration of the preferentially permeating components is varied over a wide range - from "traces" to "fairly high". The discussion of the results shows clearly the importance or unimportance of the resistances relative to each other for every process. Finally, the effect of transport resistances on module performance is discussed.