The Proastiakos is Greece's Commuter rail service, run by Hellenic Train, on rail infrastructure owned by the Hellenic Railways Organisation (OSE) (lines) and GAIAOSE. These services connect a participating city's central railway station to important locations such as a city's port or airport, as well as its suburbs and occasionally nearby towns and cities.

Hellenic Train S.A., formerly TrainOSE S.A., is a private railway company in Greece which operates passenger and freight trains on OSE lines. Hellenic Train employs train crews, operators and manages most of the rail services throughout the Greek railway network, leasing rolling stock owned by GAIAOSE except for ETR 470 trains.