Greek National Road 83 (), abbreviated as the EO83, is a national road in Attica, Greece. The EO83 is an inverted U-shaped road that runs between Athens and Rafina, via Marathon Dam and Marathon.
The EO83 is officially defined as an inverted U-shaped road in Attica: it branches off the EO54 at Ampelokipoi in Athens, and passes through Kifissia (via Kifisias Avenue), Agios Stefanos (Oeum) and Marathon, before meeting the EO54 at a junction west of Rafina. The section between Marathon and Rafina is on the route of the Athens Classic Marathon, with the remainder of the race route mostly along the EO54.
Ministerial Decision G25871 of 9 July 1963 created the EO83 from the old EO8, which existed by royal decree from 1955 until 1963, and followed the same route as the current EO83.
Part of the planned extension of Athens Metro Line 4 from to may run under or parallel to the EO83, between the Faros and OTE stations.