The Earth's temperature distribution is intimately connected to problems of the structure, composition, dynamic state, and evolution of the planet. The high temperatures in the interior provide the driving force for the Earth's convective engine and are ultimately responsible for the vigorous geological activity on the surface of the planet. The past quadrennium has witnessed major advances in our understanding of the thermal structure of the Earth. In this short review of primarily U. S. work, only a few highlights of recent advances can be summarized. While considerable progress has been made, a number of aspects of the Earth's temperature structure remain highly controversial.