Third rail railways predominantly operates in urban areas. Notable exceptions are (or were) mainline electrics of the former Southern Region of British Railways and a few interurban railways in the US. In Europe top contact third rail tends to be limited to early electrified urban railways (the current conductor is normally left naked on top), contrary to North America where it usually has a protecting cover. Considered safe, the covered top contact conductor also appeared at most North American systems built relatively recently. Modern European systems predominantly make use of bottom or side contact power rails.

There are numerous urban rail systems, including these running mostly in tunnels, which do not use third rail at all. Such systems can be found in Asia, which may have been influenced by the overhead power supply formula followed by Tokyo Metro after 1960. All South Korean systems use overhead wires (or rigid conductors), as do most modern mainland Chinese metros. In Europe all significant Spanish systems now have overhead power supply. Modern Latin America urban rail also uses overhead wires, though with some important exceptions.

Special group of bottom power supplied railways are rubber-tyred systems. In fact, it may be difficult to classify them beyond any doubt. They may be trains but are they still railways? And do they still have 'third' rails? Despite doubts, such guided systems have been included in the list below.

The list does not include conduit system trams (trolleys), once quite popular in some countries, but none survive.