Quantum-mechanical transport effects become important in the operation of nanoscale devices. Understanding quantum phenomena, such as tunneling and phase coherent wave-like transport, not only provides better description of device characteristics, but also paves the foundation for novel class of devices. The electron spin, a purely quantum mechanical quantity, offers an independent degree of freedom in contrast to the electronic charge. By exploiting spin we can potentially surpass the existing downscaling limitations and generate new opportunities for making ultra-dense, high-speed, low-power computing and memory devices. Spin-electronics ("spintronics") research is already accelerating the development of quantum computing, quantum cryptography, molecular electronics and sensors. While existing semiconductor devices operate in the diffusive transport regime where scattering results in heat dissipation and limits frequency response, spin transport in the ballistic regime offers opportunities which are as yet unexplored and unexploited.