Heat, or thermal energy, is one of the three ingredients essential to fire-the other two are oxygen and fuel. Enough oxygen for fire is almost always available in wildlands, and fuel is usually plentiful. But the mere presence of a heat source does not necessarily result in a wildland fire. Before a hot or flaming firebrand can ignite the fuel, some of its heat must be imparted to the fuel in some way. And for a fire to continue to burn and to spread, heat must be transferred from the fire to unburned fuel. Heat can move from one point to another in three basic ways: by conduction, by radiation, or by convection. Most often, all three methods of heat transfer are operating at the same time in a wildland fire. In the following discussion, we will examine the characteristics of one of these methods by which heat can move-the transfer of heat by conduction. 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.