The Hellenic Railways Organisation or OSE (Greek: Οργανισμός Σιδηροδρόμων Ελλάδος, romanized: Organismos Sidirodromon Ellados or Greek: Ο.Σ.Ε.) was the Greek national railway company which owned, maintained and operated all railway infrastructure in Greece with the exception of Athens' rapid transit lines from 1971 to 2025. Services on these lines are run by Hellenic Train., a former OSE subsidiary, Rail Cargo Logistics Goldair, Pearl and Grup Feroviar Român.