Mo-Si-B intermetallics consisting of the phases Mo3Si, Mo5SiB2, and α-Mo (Mo solid solution) can be designed to exhibit some degree of oxidation resistance, fracture toughness, and creep strength, but not necessarily all of these at the same time. For example, microstructures that enhance the oxidation resistance are typically associated with low fracture toughness. Examples will be given illustrating the oxidation resistance, fracture toughness, and creep strength of Mo-Si-B intermetallics as a function of their phase volume fractions as well as the topology and length scale of their microstructures. Microstructures containing either individual α-Mo particles or a continuous α-Mo matrix will be described. The examples provide possible ways to control the composition and microstructure of Mo-Si-B alloys such as to optimize the desired balance of properties.