Wildland fire is dependent on heat transfer. For a fire to start, heat must be transferred from a firebrand to the fuel. If the fire is to burn and grow, heat transfer to the unburned fuel around the fire must continue. The way a fire burns and behaves is closely related to the manner and rate of heat transfer. The speed with which fire spreads, for example, depends greatly on how quickly sufficient heat for ignition can be transferred to the unburned fuel. Heat can be transferred from one point to another in three ways-by conduction, by radiation, or by convection. In Parts 1 and 2 of this series, the nature of heat and transfer of heat by conduction were examined. Here we discuss heat transfer by radiation. The level of difficulty of the treatment of topics in these publications varies, as signaled by the color of the cover: the blue cover group is generally elementary and the yellow cover group is intermediate.