A consistent description of all the diffusive processes is obtained by the Thermodynamics of Irreversible Processes. The values of isothermal diffusion and Soret coefficients must however be determined on different grounds. The determinations obtained by numerous theories and ground-based measurement techniques do not provide reliable results. From the experimental point of view, it is now recognized that groundbased measures are affected in an unpredicted way by convection. The data obtained in M G therefore provide very relevant data for both experimental and theoretical developments. Such developments are to be pursued with the tools provided by the M G conditions in view of the new perspectives that they open. Precise data to quantify processes in both fundamental and applied research are urgently needed.