Greek National Road 51 (Greek: Εθνική Οδός 51, abbreviated as EO51) is a predominantly single carriageway road in the Evros regional unit of Greece.

[1] The EO51 is officially defined as a branch of the EO2 from Ardani (about 40 km east of Alexandroupolis) to the Greece–Turkey border between Kastanies and Edirne (Adrianopolis), via Soufli, Didymoteicho and Orestiada.

[2] The EO51 generally runs parallel to the Evros river on the western bank, up towards Kastanies: the EO51 then turns east, south of the Arda river, to meet the D.100 road at the Greece–Turkey border, towards Edirne.

There is an interchange with the A2 motorway (Egnatia Odos), 2 km north from the southern end of the EO51.

[6] Greece adopted the current E-road numbering system on 9 January 1989, when it joined the 1975 European Agreement on Main International Traffic Arteries (AGR).