OSE came into existence on 1 January 1971 through Legislative Decree 674/1970, inheriting the assets and debts of the Hellenic State Railways, which had been founded in 1920. The new organization took on a challenging inheritance. Greece's terrain — mountains, gorges, narrow coastal plains — had always made rail construction expensive. The backbone of the network, running from Patras through Athens to Thessaloniki and onward to the Bulgarian and Turkish borders, covered 520 kilometers on the Athens–Thessaloniki main line alone. A tangle of metre-gauge lines served the Peloponnese and parts of Thessaly. OSE's first logo featured a winged wheel — speed and connection rendered in simple graphic form — and its early rolling stock was painted in functional shades of green, consistent with European railway practice of the era.

The 1990s and 2000s brought a cascade of organizational changes. ERGOSE was created in 1996 to manage infrastructure projects. GAIAOSE followed in 2001 to handle stations and property. TrainOSE emerged in 2005 as the passenger-facing brand. The Athens suburban network, Proastiakos, was launched ahead of the 2004 Olympic Games to give the capital the kind of commuter rail service it had long lacked. Then came the financial crisis. Greece's debt catastrophe forced the sale of state assets, and TrainOSE was privatized: in July 2016, Italy's Ferrovie dello Stato Italiane submitted the only binding offer of €45 million, completing the purchase in September 2017. The Italian group later rebranded the operation as Hellenic Train. Liveries shifted from the old blue-and-white of Greek national colors to the red-and-silver of an Italian-influenced corporate identity.

On 28 February 2023, two passenger trains collided head-on near Tempi, in the gorge of the Peneios River — a tragedy that exposed failures in safety systems and worker training that no organizational chart could obscure. Then, on 5 September 2023, Storm Daniel swept through Thessaly, destroying approximately 50 kilometers of track and washing away bridges and signaling equipment in areas around Domokos, Doxaras, and Paleofarsalos. Repair estimates ran between 35 and 50 million euros. By 2025, Deutsche Bahn had signed an agreement to assist with modernization, deploying German engineers and specialists to support Greek operations. In August 2025, the Greek Ministry of Infrastructure and Transport announced the creation of a new body — Greek Railways — consolidating OSE, ERGOSE, and GAIAOSE into a single structure. The mandate: safety first, modernization second, and the lessons of Tempi never to be forgotten.

To understand OSE is to follow its tracks across Greece's improbable terrain. The main line from Athens climbs through Thebes and Larissa before descending to Thessaloniki — the InterCity express covers the 520 kilometers in about four hours. A branch serves Volos and the Pelion coast. Another curves west through Karditsa and Trikala to Kalabaka, where passengers arrive within sight of the monasteries of Meteora, perched on their sandstone pillars above the plain. In the Peloponnese, the old metre-gauge network reached Patras, Kalamata, Nafplion, and Olympia — though passenger services on most of these lines were suspended in 2011 and remain dormant. The famous Diakofto–Kalavryta rack railway, climbing 720 meters in 22 kilometers through the Vouraikos Gorge, survives as both heritage line and working tourist attraction.

That first logo — the winged wheel — carried a certain ambition. Greece had connected itself to the European railway network in 1916 when the line from Athens reached Platy, linking it to the continent. A century later, that connection remains essential but fragile. The electrified standard-gauge line from Athens to Thessaloniki is the spine of the modern system; everything else is either being upgraded or awaiting funds to do so. The new airport line, inaugurated in 2004, runs double-track and electrified to Athens International. Plans exist to extend the network to Rio, to eventually reach Patras by fast train, and to reconnect with Istanbul along the Eastern Egnatia corridor. The ambition is unchanged. The work is only beginning.