It was possible to describe large number of processes such as melting, solidification, microwave thawing, spray-drying, and freeze-drying by a single theoretical model. All these applications and some others have one thing in common, that is the formation of a moving interface during the process of heat and mass transfer. This interface may be defined by a sharp boundary or by a region, depending on the application considered. The unsteady-state heat conduction equation was found to describe well the transport of heat in these processes. Two different numerical solutions have been developed, one for the sharp interface and the other for materials that undergo phase transformation within a range of temperatures. In spite of the large variation in the applications considered in this paper, the agreement was good between the theoretical predictions and our experiments, and some of the measurements available in the literatures.