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Abstract: The dissolution of Fe3C in ferrite has been shown to be controlled by a slow first order interfacial reaction. The rate constant,K, is Arrhenius in behavior and involves two activation enthalpies; one applies to a jump process with a short relaxation time, another to a long relaxation time process which is tentatively identified as a change in kink density on ledges in the interface. The heat of solution of Fe3C in ferrite also appears in the exponential. A single process, activated jump theory is not adequate to explain the behavior ofK with temperature; a dissolution model based on a ledge-double kink mechanism appears to be in agreement with experiment. These features point to significant differences between the mechanism of interphase boundary migration and grain boundary migration. In addition, the Fe3C-ferrite interface is felt to be at equilibrium with respect to carbon but not iron, leading to small departures from stoichiometry in the Fe3C at the interface.