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This article discusses three main points. First, ultrahigh-temperature materials offer a large return to the propulsion community and to the economy, but replacing Ni-based alloys is a very difficult problem for both technical and financial reasons. Second, the oxidation resistance of selected Mo-Si-B alloys and the prospects for combining this with useful structural properties are remarkable, given the nature of conventional Mo alloys; however, there are nagging issues associated with their low-temperature (∼700°C) behavior. Third, further advances in the processing of such materials, together with assessments of their affordability and reliability, are vital for achieving a successful engineering technology.