Core-shell nanowires are cylindrical structures consisting of an internal core and an external shell of different materials, typically semiconductors, of diameter below 100 nm. Three mechanisms of electron localization, experimentally observable, will be discussed. 1. With an insulating shell and a thin conductive core the charge carriers are radially localized and the electronic transport occurs through a tube. In the presence of a longitudinal magnetic field the angular motion of the electrons leads to conductance oscillations related to the Aharonov-Bohm (AB) effect. 2. A magnetic field perpendicular to the nanowire produces angular localization, along the two sides lateral to the magnetic field, where the electron distribution has maxima, around the so called snaking orbits. Another type of AB oscillations can be obtained in this case. 3. Due to the original crystalline structure of the materials used for fabrication the resulting cross section of the nanowires is usually not circular, but polygonal. The electronic ground state is localized in the corners, and the transitions to the excited states localized on the sides correspond to optical transitions over a broad energy interval.