Hellenic State Railways or SEK was a Greek public sector entity which was established on 18 March 1920 by the law 2144/20 and operated most Greek railway lines until 1970.

Rail transport in Greece has a history which began in 1869, with the completion of the then Athens & Piraeus Railway. From the 1880s to the 1920s, the majority of the network was built, reaching its heyday in 1940. From the 1950s onward, the railway system entered a period of decline, culminating in the service cuts of 2011. Ever since the 1990s, the network has been steadily modernized, but still remains smaller than its peak length. The operation of the Greek railway network is split between the Hellenic Railways Organisation (OSE), which owns and maintains the rail infrastructure; GAIAOSE, which owns the building infrastructure and the former OSE rolling stock, Hellenic Train; and other private companies that run the trains on the network. Greece is a member of the International Union of Railways (UIC). The UIC Country Code for Greece is 73.