Saint-Jean-de-Luz (French: [sɛ̃ ʒɑ̃ d(ə) lyz]; Occitan: Sent Joan de Lutz; Basque: Donibane Lohitzune, locally Donibane Lohizune [doniˈβane lohiˈs̻une]) is a commune in the Pyrénées-Atlantiques department, southwestern France. Saint-Jean-de-Luz is part of the former Basque province of Labourd (Lapurdi).

Saint-Jean-de-Luz is a fishing port on the Basque coast and now a famous resort, known for its architecture, sandy bay, the quality of the light and the cuisine. The town is located south of Biarritz, on the right bank of the river Nivelle (French for Urdazuri) opposite to Ciboure. The port lies on the estuary just before the river joins the ocean. The summit of Larrun is about 8 km (5 mi) south-east of the town. The summit can be reached by the Petit train de la Rhune, which starts from the Col de Saint-Ignace, 10.5 km (6.5 mi) east of the town on the D4 road to Sare. It is in the traditional province of Lapurdi of the Basque Country.

Saint-Jean-de-Luz bay is a natural harbour in the south-east of the Bay of Biscay. It is the only sheltered bay between Arcachon and Spain. Thanks to its strong sea walls or dykes that protect the town from the full savagery of the Atlantic Ocean, it has become a favorite for bathers across the Basque Coast. Although the seaside resort is relatively recent, the port itself is centuries old, with the most prominent point in its history being the marriage in 1660 of Louis XIV and the Spanish princess Maria Teresa.

Water from the area flows into the town from the Nivelle and its smaller tributaries, the Etxeberri, Isaka and Xantako streams. There is also the Basarun, and its smaller tributary the Mendi, which passes directly through Saint-Jean-de-Luz. The river has been made accessible to boats and it joins the sea by the Erromardia beach. A branch of the Uhabia, an emblematic river in the neighbouring Bidart district, and its smaller Amisola tributary, also pass to the sea through St Jean de Luz.^{[citation needed]}

Saint-Jean-de-Luz straddles Route départementale D810, the old Route nationale 10. The town can be reached from the A63 motorway, Exit 3 (Saint-Jean-de-Luz Nord) and Exit 2 (Saint-Jean-de-Luz Sud). The Saint-Jean-de-Luz-Ciboure station is served by the SNCF Bordeaux–Irun railway. Biarritz Airport is the closest airport to Saint-Jean-de-Luz.

Saint-Jean-de-Luz is the French adaptation of the Labourdine Basque Donibane Lohizune – from done 'saint', Ibane 'John' and lohi 'mud' + -z 'made of' + -une 'place of'; thus meaning 'Saint John's swamp'. It is a common misconception that Luz would be the Spanish word for 'light'.

The town is named after the frequent floodings which occurred in the area over the centuries.

Saint-Jean-de-Luz is located on the Atlantic coast of France, just a few kilometres from the border with Spain. Its wealth stems from its port and its past, with the town being associated with both fishing, and with the capture of vessels by its own Basque corsaires, or pirates (English sailors used to call Saint-Jean-de-Luz the "Viper's Nest"). This prosperity reached its height during the 17th Century, which is still considered as the town's "Golden Age." During this period, Saint-Jean-De-Luz became the second largest town in the Labourd region with a population or around 12,000, just behind Bayonne.