The need to dope a semiconductor presents several challenges when going to the nanoscale. On the one hand, there is an intrinsic technological problem of carrying out the doping process. Standard approaches used in microelectronics such as ion implantation can be difficult to govern when dealing with nanowires, whereas dopant incorporation at growth time seems to be bedeviled by the surface segregation and inhomogeneous axial distribution along the wire. On the other hand, in the quantum confinement the band gap is known to broaden as the wire diameter shrinks: what happens to donor and acceptor levels in such a regime? The ability of creating differently doped regions is at the core of device design and these problems must be solved before significant progresses in ultra-thin nanowire based electronics can be made.