“Bottom up” nanowires are chemically synthesized single crystalline 1D nanomaterials with low defect density, and atomically smooth surface facets. They represent a new class of building blocks for nanoelectromechanical systems (NEMS) with high resonant frequencies and very low mechanical loss. With dimensions approaching molecular size and a small mass down to femtogram scale, nanowire resonators are expected to operate into and beyond ultra-high frequency (UHF) range, enabling single molecule mass detection sensitivity as well as observation of quantum mechanical motion. The wide choice of nanowire materials brings a variety of unique functionalities into NEMS devices. For example, single crystal piezoelectric nanowires can be used for efficient actuation and detection of mechanical motions. The generation of electrical charges from mechanical stress in piezoelectric nanowires will be able to power nanoscale integrated lab on a chip systems.