The Gulf of Euboea, Euboean Gulf, Euboic Sea or Euboic Gulf (modern Greek: Ευβοϊκός Κόλπος, Evvoïkós Kólpos) is an arm of the Aegean Sea between the island of Euboea (northeast coastline) and the Greek mainland (southwest coastline). Trending diagonally northwest-southeast, the gulf is divided by the narrow Strait of Euripus, at the town of Chalcis (Khalkís).