© 2018 Elsevier Inc. Piezoelectric semiconducting nanowires have generated much interest due to the interplay of their mechanical, electrical, and optical properties, which paves the way for potential applications in mechanical energy harvesting as well as sensing. The nature of piezoelectricity in these nanowires is governed by the crystalline phases present, which in turn can be controlled during the nanowire growth process. This chapter provides insight into the manifestation of piezoelectricity in semiconducting nanowires, the effect of growth on their piezoelectric properties, and importantly, how piezoelectricity is characterized at the nanoscale in these materials. Energy-related applications of semiconducting piezoelectric nanowires are described in detail, including their incorporation into nanogenerators for energy harvesting, as well as in piezotronic and photo-piezotronics devices based on the electromechanical and opto-electromechanical interactions taking place in piezoelectric semiconductor-nanowire junction-based devices. Advances in nanofabrication, nanoscale characterization, and device engineering, coupled with a greater understanding and control of piezoelectricity in semiconducting nanowires, will ultimately help unlock the full potential of these fascinating nanomaterials.