The use of Mo base alloys is limited by severe oxidation above about 650 8C. While MoSi 2 coatings offer protection at high temperature, they are ineffective at low temperature. An integrated coating design has been developed based upon (B þ Si) co-deposition and an in-situ diffusion barrier that offers robust, long term oxidation protection and self-healing for Mo alloys over a wide temperature range to over 1600 8C.In recognition of the need for increased operating temperatures in order to satisfy the demands for increased gas turbine engine performance and improved energy efficiency that cannot be satisfied by Ni-base superalloys, new ultrahigh temperature structural materials in refractory metal systems and ceramic materials are under study. [1] Within these efforts, alloys in the MoÀSiÀB system have been identified with a number of attractive features based upon strength and creep resistance. [2][3][4][5] The base system does develop a protective borosilica oxidation scale, but the alloy recession rate that is too high for desired lifetimes. [6] For structural applications, the requirements for high strength at high temperature along with environmental attack resistance are not usually satisfied concurrently for most materials. One effective strategy to address an enhanced resistance to environmental attack in high strength materials is the application of oxidation resistant coatings. While this strategy is attractive, the successful implementation of protective coatings over the entire operating temperature range requires the satisfaction of other requirements involving thermodynamic and mechanical compatibility between the coating and the alloy substrate and the robust stability of the coating in order to maintain the integrity of the environmental protection.For the development of a coating design, the first step is to identify the key compositional and kinetic factors controlling the oxidation response. In the current work, this has been accomplished by analyzing the oxidation products and the reaction pathway as a basis for applying a novel kinetic biasing strategy to control the coating phase structure and sequencing and enhance the oxidation resistance. The approach for refractory metals is illustrated first for MoÀSiÀB ÀB alloys where the key components of the coating design are identified and then extended to other Mo-base systems.