Semiconductor nanowires have attracted great interest due to their potential application in optically active devices, as building blocks for nanocircuitry and in energy conversion devices, for which electron and phonon transport play a significant role in determining their properties.In particular, group IV nanowires, such as Si and Ge, are playing a big role in the development of new functional microelectronic modules, such as gate-all-around field-effect transistor devices, on-chip lasers and photodetectors. Recently there has been a renewed interest in Ge for applications such as nanoelectromechanical systems (NEMS), lithium-ion batteries, field effect transistors (FETs) and photovoltaics. Like Si, Ge is a group IV semiconductor material and exhibits certain properties that are superior to those of Si, including a higher charge carrier mobility and a larger Bohr exciton radius, leading to more pronounced quantum confinement effects at higher dimensions. Notably, the many parallels between Si and Ge should allow the seamless integration of Ge into current Si based devices.