For Pontic Olbia, the Greek colony on the Black Sea coast, see Olbia, Ukraine.

Olbia (locally "Terranoa" in the Sardinian language or "Tarranoa" in Gallurese), is a town of approximately 40,000 inhabitants in northeastern Sardinia (Italy), in the Gallura sub-region.

Called "Olbia" in the Roman age, "Civita" in the Middle Ages (Giudicati period) and "Terranova Pausania" before the 1940s, Olbia was again the official name of the town after the period of Fascism. It is the economic centre of this part of the island (commercial centres, food industry) and is very close to the famous Costa Smeralda tourist area. It will soon become an administrative capital (together with Tempio Pausania) of the new province of "Olbia-Tempio".

It is the main connection between Sardinia and the Italian peninsula, with an airport ("Olbia-Costa Smeralda"), a passenger port (Olbia-Isola Bianca), and a railway to Porto Torres and Cagliari. There are an expressway to Nuoro and Cagliari (SS131) and national roads to Sassari (SS199-E840), Tempio Pausania (SS127), and Palau (SS125).

Olbia (the name is of Greek origin) is very ancient and was possibly founded by the Greeks, according to a local legend. It contains ruins from prehistoric times (Phoenician settlement) to the Roman Era, when it was an important port, and the Middle Ages, when it was the capital of the Giudicato of Gallura, one of the four independent states of Sardinia. Also notable is the Romanesque former cathedral of San Simplicio (11th-12th century).