Our paper about inorganic halide perovskite nanowire multi-color heterojunctions has been published on PNAS. Halide perovskites are promising semiconductor materials for solutionprocessed optoelectronic devices. Here, we show that the anion-exchange chemistry can be precisely controlled in single-crystalline halide perovskite nanomaterials when combined with nanofabrication techniques. We demonstrate spatially resolved multicolor CsPbX3 (X = Cl, Br, I, or alloy of two halides) nanowire heterojunctions with a pixel size down to 500 nm with the photoluminescence tunable over the entire visible spectrum. This work is highlighted by LBNL news and many others.