The Gulf of Piran or Piran Bay (, or , ) is located in the northern part of the Adriatic Sea, and is a part 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 . Since the 1990s, the name Bay of Savudrija (Savudrijska vala) has also been used in Croatia.
On the eastern Slovenian coast lie the towns of Piran, 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 .