Au-catalyzed In x Ga 1- x As nanowires (NWs) and In x Ga 1- x As/GaAs core-shell NWs were grown by molecular beam epitaxy on (1 1 1)B GaAs. The effects of In content, growth temperature, and V/III elemental flux ratios on NW morphology have been investigated. The structure of the NWs has been characterized by SEM and transmission electron microscopy and their optical properties by low-temperature photoluminescence.