The importance of nanoelectronics is enormous given the constant demand for enhancement in performance of electronic and computing devices. While Moore's law predicted the exponential increase in the power of processing units, the associated device level physics have brought about a new set of interdisciplinary challenges. Miniaturization of transistors has been the key to the unprecedented growth of microelectronics and its gradual transition to lower length scales. However, system sizes at the nanoscale being comparable to the mean free paths of the charge carriers (electrons), additional considerations in the transport processes need to be accounted for to obtain a thorough understanding of the operation of these molecular scale devices. The fundamental operating principles though similar, issues related to ballistic transport and wave nature of electrons, effects of tunneling etc., become significant at such small system dimensions.