Semiconductor nanowires are "needle"-like nanostructures that have unique materials, electronic and optical properties that render them promising for next-generation applications in fields like optoelectronics, energy systems and life sciences. An intensive and worldwide research effort in the field of nanowires was launched in the late 1990s, about 10 years after the pioneering work by Dr. Hiruma at Hitachi in Japan. In my research group we spent the first five years on fundamental studies of the materials growth and the materials physics of nanowires, especially heterostructure systems, while in parallel also developing novel methods that combined top-down patterning with bottom-up self-assembly, to enable the reproducible fabrication of perfectly ordered nanowire arrays. From around 2005, it became evident that this blue-sky research offered significant advantages and opportunities for various applications, primarily in enabling high-speed and optoelectronics devices by monolithic integration of III–V nanowires with silicon. We have also explored ways in which these nanostructures can be used for energy scavenging and in applications that enable energy conservation.