The Gulf of Piran or Piran Bay (Slovene: Piranski zaliv, Croatian: Piranski zaljev or, recently, Savudrijska vala, Italian: Baia di Pirano) is located in the northern part of the Adriatic Sea, and is a part of the Southernmost tip of the Gulf of Trieste. It was named after the town of Piran, and its shores are shared by Croatia and Slovenia. It is delimited by a line connecting Cape Savudrija (Savudrijski rt) in the south to the Cape Madona (Rt Madona) in the north and measures around 19 square kilometres (7.3 sq mi). Since the 1990s, the name Bay of Savudrija (Savudrijska vala) has also been used in Croatia.

On the eastern Slovenian coast lies the town of Piran, and the settlements Portorož and Lucija. On the southern Croatian coast are tourist camps of Crveni vrh and Kanegra, built in the 1980s. The main river flowing into the gulf is the Dragonja, whose mouth is on the border. Along the mouth of the Dragonja lie the Sečovlje saltpans, covering an area of 650 hectares (1,600 acres).

The Gulf area has been a theatre of a maritime and land border dispute between Slovenia and Croatia.

Piran (Italian: Pirano) is a town in the eponymous municipality in southwestern Slovenia on the Gulf of Piran on the Adriatic Sea. It is one of the three major towns of Slovenian Istria. The town resembles a large open-air museum, with medieval architecture and a rich cultural heritage. Narrow streets and compact houses give the town its special charm. Piran is the administrative centre of the local area and one of Slovenia's major tourist attractions.

In the pre-Roman era, the hills in the Piran area were inhabited by Illyrian Histri tribes who were farmers, hunters and fishermen. They were also pirates who disrupted Roman trade in the north Adriatic Sea. The Piran peninsula was incorporated into the Roman Empire in 178 and 177 BC and settled in the following years with rural homes (ville rusticae).

The decline of the Empire, from the 5th century AD onwards, and incursions by the Avars and Slavs at the end of the 6th century, prompted the Roman population to withdraw into easily defensible locations such as islands or peninsulas. This started local urbanisation and by the 7th century, under Byzantine rule, Piran had become heavily fortified. Despite the defences, the Franks conquered Istria in 788 and Slavs settled in the region. By 952, Piran had become a part of the Holy Roman Empire. The earliest reliable records of the area are in the 7th century work Cosmographia by an anonymous cleric of Ravenna. The name of the town most probably originates from the Greek "pyrranos", which means "red", because of the reddish flysch stones commonly found in the town's area.