Abstract: Heat storage and transfer system and method in which a liquid-solid phase change material and a liquid-vapor phase change material selected for coaction with each other are disposed in a container with a body of the liquid phase of the liquid-vapor material in continuous contact with a body of the liquid phase of the liquid-solid material for superior heat transfer between the materials for giving up and transferring sensible heat and liquid to solid phase change latent heat to vaporize liquid-vapor phase change material and vapor to liquid phase change latent heat to a condenser/heat exchanger and also for superior heat transfer from a heat source such as a solar or electric heater by giving up the heat of condensation of a vapor phase to a solid-liquid material which accepts the heat as sensible heat and as heat of melting.