The processes of solid-liquid phase change, during which the heat is alternatively charged into the system and discharged from it, involve a combination of different physical phenomena. In this section, an overview of these effects is presented. The main methods of heat transfer analysis are introduced, and the main methods of multidimensional numerical simulation are discussed. Several examples, invoking the basic configurations used in or suggested for the latent-heat based thermal energy storage systems, are presented and described. Current research issues are outlined, with a special attention to unresolved and outstanding problems.