Istria, formerly Histria (Latin), Ίστρια (Ancient Greek), is the largest peninsula in the Adriatic Sea. The peninsula is located at the head of the Adriatic between the Gulf of Trieste and the Kvarner Gulf. It is shared by three countries: Croatia, Slovenia, and Italy. Croatia encapsulates most of the Istrian peninsula with its Istria County (Regione istriana in Italian).
The geographical features of Istria include the Učka mountain ridge, which is the highest portion of the Ćićarija mountain range; the rivers Dragonja, Mirna, Pazinčica, and Raša; and the Lim bay and valley. Istria lies in three countries: Croatia, Slovenia and Italy. By far the largest portion (89%) lies in Croatia. "Croatian Istria" is divided into two counties, the larger being Istria County in western Croatia. Important towns in Istria County include Pula/Pola, Poreč/Parenzo, Rovinj/Rovigno, Pazin/Pisino, Labin/Albona, Umag/Umago, Motovun/Montona, Buzet/Pinguente, and Buje/Buie. Smaller towns in Istria County include Višnjan, Roč, and Hum. The northwestern part of Istria lies in Slovenia: it is known as Slovenian Istria, and includes the coastal municipalities of Piran/Pirano, Izola/Isola and Koper/Capodistria, and the Karstic municipality of Hrpelje-Kozina. Northwards of Slovenian Istria, there is a tiny portion of the peninsula that lies in Italy. This smallest portion of Istria consists of the comunes of Muggia and San Dorligo della Valle, with Santa Croce (Trieste) lying farthest to the north. The ancient region of Histria extended over a much wider area, including the whole Kras plateau until the southern edges of the Vipava Valley, the southwestern portions of modern Inner Carniola with Postojna and Ilirska Bistrica, and the Italian Province of Trieste, but not the Liburnian coast which was already part of Illyricum.