Oswestry (/ˈɒzwəstri/ OZ-wəss-tree; Welsh: Croesoswallt) is a market town, civil parish and historic railway town in Shropshire, England, close to the Welsh border. It is at the junction of the A5, A483 and A495 roads.

The town was the administrative headquarters of the Borough of Oswestry until that was abolished in 2009. At the 2021 Census, the population of Oswestry was 17,509. The town is five miles (8.0 km) from the Welsh border and has a mixed English and Welsh heritage.

Oswestry is the largest settlement within the Oswestry Uplands, a designated natural area and national character area.

The name Oswestry is first attested in 1191, as Oswaldestroe. This Middle English name transparently derives from the Old English personal name Ōswald and the word trēow ('tree'). Thus the name seems once to have meant 'tree of a man called Ōswald'. However, the traditional Welsh name for the town, Croesoswallt (first attested in 1254), means 'Oswald's cross', and 'cross' is a possible meaning of Old English trēow. Thus the town's name may have meant 'Oswald's cross' in both English and Welsh.

The Oswald mentioned is widely imagined to have been Oswald of Northumbria, who died at the Battle of Maserfield in 641/642. The location of the battle is debated among scholars, but for much of the twentieth century was assumed to be at Oswestry. However, A. D. Mills's Dictionary of English Place Names concluded that 'the traditional connection with St Oswald, 7th-century king of Northumbria, is uncertain'.

The name and the association with King Oswald have attracted more fanciful interpretations. According to legend, one of the dismembered Oswald's arms was carried to an ash tree by a raven. Miracles were subsequently attributed to the tree, and the legend has it that this was "Oswald's Tree", and gave its name to the town. A spring called 'Oswald's Well' is supposed to have originated where the bird dropped the arm from the tree, though one historian has suggested that it was likely to have had sacred associations long before Oswald's time. The water from the well was believed to have healing properties, particularly for curing eye trouble. Offa's Dyke runs near the well, to the west. This interpretation is supported by a passage in Fouke le Fitz Waryn (a 13th-century romance) which states that Oswaldestré was derived from Arbre Oswald (Oswald's tree), which in turn was changed from La Blanche Launde (Welsh: y tir Gwyn), which belonged to a Briton called Meredus Fitz Beledyns (Maredudd ap Bleddyn).

There is an alternative view that Oswestry was named after Oswy, Oswald's brother, who fought a battle here against King Penda in 655 AD. Oswy became King of Northumbria after Oswald's death in 642 AD. The battle of 655 AD was fought near to a river called the Winwead, which it is believed, was the nearby River Vyrnwy. Welsh folklore has it that this battle was called the battle of Pengwern and in it their leader Cynddylan was also killed.

The earliest known human settlement in Oswestry is Old Oswestry, one of the best-preserved Iron Age hill forts in Britain, with evidence of construction and occupation between 800 BC and 43 AD. The site is known in Welsh as Caer Ogyrfan, meaning 'City of Gogyrfan', referring to the father of Guinevere in Arthurian legend.