This article reviews the most recent progress in the development of Nb-silicide-based in situ composites for potential applications in turbine engines with service temperatures of up to 1350°C. These composites contain high-strength Nb silicides that are toughened by a ductile Nb solid solution. Preliminary composites were derived from binary Nb-Si alloys, while more recent systems are complex and are alloyed with Ti, Hf, W, B, Ge, Cr, and Al. Alloying schemes have been developed to achieve an excellent balance of room-temperature toughness, fatigue-crack-growth behavior, high-temperature creep performance, and oxidation resistance over a broad range of temperatures. Nb-silicide-based composites are described with emphasis on processing, microstructure, and performance. Nb silicide composites have been produced using a range of processing routes, including induction skull melting, investment casting, hot extrusion, and powder metallurgy methods. Nb silicide composite properties are also compared with those of Ni-based superalloys.