The principal contents of this final report are the essential portions of two dissertations completed by graduate students supported by this research project. One is the doctoral dissertation of T.B. Lindemer, Investigation of Methods for Calculation of Interdiffusion Coefficients. In this research, new methods were devised and investigated for using a digital computer to make calculations in the complex case of three-component systems characterized by concentration-dependent diffusion coefficients. Although main attention was given to single-phase systems, the even more difficult problem of multiphase systems was also treated. The second topic, Effect of Alloying on the Diffusion of Carbon Between Ferrite and Austenite, is the master's thesis of J.-F. Remy. The research studied the effect of additions of nickel on the diffusion of carbon in a two-phase system. Evidence was obtained that some phenomenon at the phase interface is influencing the diffusion process. (Author).