Vasto is a comune located on the Adriatic coast within the Province of Chieti in the southern Abruzzo region of Italy. The city has historical roots dating back to the Middle Ages, during which time it was known by various names including Guastaymonis, Vasto d'Aimone, and Waste d'Aimone.
During the period of Fascist Italy, the city was referred to as Istonio. It was officially renamed Vasto in 1944.