While the chemical composition of semiconducting metal, halide perovskites :can be 1 precisely controlled in thin films for photoVoltaic devices, the synthesis of perovskite nanostrilctlires with tunable dimensions and composition has not: been realized. Here, we describe the templated synthesis of uniform perovskite nanowires with controlled diameter (50-200 nm). Importantly, by providing three examples (CH3NH3PbI3, CH3NH3PbBr3, and Cs2SnI6), we show that this process is composition general and results in oriented nanowire arrays on transparent conductive substrates.