Engineering materials with better high temperature oxidation properties are needed to increase the thermodynamic efficiencies of the energy production and transportation systems. Because of their high melting temperatures, refractory metals like Nb or Mo are brought together with intermetallic compounds as two components of a new class of composite materials. To acquire a balanced high temperature mechanical and oxidation properties, these materials generally have multiphase and multicomponent structures. Borides of some transition elements are also being considered as high temperature structural materials for new aerospace vehicles. These materials are also required to have sufficient high temperature oxidation resistance in order to provide reliable and long service lives.