A theoretical study reducing the general diffusion solution in a multicomponent system to an eigenvalue problem is carried out. Certain properties of the diffusion coefficient matrix are investigated. Special solutions are obtained tor a ternary finite diffusion couple and for a moving phase boundary in an infinite medium involving diffusion on both sides or the interface. The latter solution is used to study the kinetics of the growth of proeutectoid ferrite in ternary Fe-Mn-C austenite. Information on the iron-rich corner of the ternary Fe-Mn-C phase diagram in the temperature range from 725°C to 790°C has been obtained experimentally, and the diffusion coefficient of manganese in a-iron has been determined. / Thesis / Master of Science (MS)