Semiconductor nanowires offer new opportunities for optoelectronic and spintronic nanodevices. However, their full potential is ultimately dictated by our ability to control multiple property-function relationships taking place at the nanoscale in the spatial and time domains. Only a combination of high-resolution analytical techniques can provide a comprehensive understanding of their complex functionalities. Here we describe how a multimodal hard X-ray nanoprobe addresses fundamental questions in nanowire research. Selected topics ranging from cluster formation, dopant segregation, and phase separations to quantum confinement effects are investigated with sub-100 nm spatial resolution and sub-50 ps temporal resolution. This approach opens new avenues for structural, composition and optical studies with broad applicability in materials science.