The Gulf of Aden (Arabic: خليج عدن; Somali: Gacanka Cadmeed) is a deepwater gulf of the Indian Ocean between Yemen to the north, the Arabian Sea to the east, Djibouti to the west, and the Guardafui Channel, the Socotra Archipelago, Puntland in Somalia and Somaliland to the south. In the northwest, it connects with the Red Sea through the Bab-el-Mandeb strait, and it connects with the Arabian Sea to the east. To the west, it narrows into the Gulf of Tadjoura in Djibouti. The Aden Ridge lies along the middle of the gulf, and tectonic activity at the ridge is causing the gulf to widen by about 15 mm (0.59 in) per year.
The ancient Greeks regarded the gulf as one of the most important parts of the "Erythraean Sea". It later came to be dominated by Muslims, as the area around the gulf converted to Islam. From the late 1960s onwards, there was an increased Soviet naval presence in the Gulf. The importance of the Gulf of Aden declined while the Suez Canal was closed, but it was revitalized when the canal was reopened in 1975, after being deepened and widened by the Egyptian government.