National Road 42 () is a highway in northwestern Aetolia-Acarnania and in Lefkada, Greece. It links the town of Lefkada with the Greek National Road 5 (Antirrio - Arta - Ioannina) in Amfilochia, passing through the town of Vonitsa.
The eastern part of the GR-42, between Amfilochia and Vonitsa, runs along the southern shore of the Ambracian Gulf. The highway contains a bridge over the Vonitsa Lagoon. A drawbridge form the connection of the island of Lefkada to the mainland. The road ends in the town of Lefkada.
The GR-42 passes through the following towns (ordered from west to east):
Ministerial Decision G25871 of 9 July 1963 created the EO42 from most of the old EO19 (between Amfilochia and Lefkada), which existed by royal decree from 1955 until 1963: in 1995, the Actium branch of the old EO19 became part of the unnumbered national road between Igoumenitsa and Vonitsa.