The optical properties of semiconductor nanowires are both important from a fundamental materials physics standpoint and necessary to understand in engineering applications: nanowire photovoltaic devices, sensors, and lasers, among others, could all benefit. Unfortunately, these optical properties are not easy to ascertain. Transmission times are short, in-coupling of white probe light is difficult, and the angle-resolved measurements typically used to determine material dispersion relations in bulk materials are hindered by diffraction effects at subwavelength nanowire end facets. Here, we present a series of experimental techniques and theoretical models developed to study of the optical properties of active nanowire waveguides. Beginning with a technique for determining the waveguide dispersion of individual ZnSe nanowires, we demonstrate enhanced properties with respect to bulk material. After investigating propagation loss in individual CdS nanowires, the theoretical model was then refined to quantify the strength of light-matter coupling, where size-dependence was observed. The knowledge gained from these studies was put to use in the first demonstration of all-optical switching in individual semiconductor nanowires. The switch concept was then extended into an all-optical nanowire NAND gate. These developments highlight the importance of semiconductor nanowires as both model materials systems and novel devices.