The Proastiakos (Greek: Προαστιακός, English: 'suburban') is the collective name for Greece's suburban railway (commuter rail) services, which are run by TrainOSE, the country's only rail operator, on infrastructure owned by the Hellenic Railways Organisation (OSE).
As of March 2016 there are three Proastiakos networks, servicing the country's three largest cities: Athens, Thessaloniki and Patras, providing them with commuter rail links towards their suburbs and also with regional services to other cities and towns.
In Athens, As of 1/8/2017 the lines between central station of Athens and Halkida have been electrified allowing EMU train service. The lines have been changed making the central station of Athens the main layover station.Those lines are Athens – Airport , Athens – Kiato , Athens – Chalkida and a DMU service Piraeus – Athens. Future changes are going to be announced when the Pireus-Athens line is electrified.
Photography and video-taking is permitted across the whole Proastiakos network, however very often the security personnel might create problems to photographers.
The term Proastiakos, which translates as "suburban", is derived from the ancient Greek word "proasteion" (suburb, προάστειον), "pro + asty (προ-άστυ)" meaning "before the city". However the same brand name has also been used for some regional rail services.