Port Stephens is a large natural harbour of approximately 134 square kilometres (52 sq mi) located in the Hunter Region of New South Wales, Australia. It lies within the Port Stephens-Great Lakes Marine Park and is situated about 160 kilometres (99 mi) north-east of Sydney. A narrow entrance between two striking hills of volcanic origin marks the opening of Port Stephens to the sea. The southern headland, Tomaree or South Head, rises to 120 metres (390 ft) above mean sea level while Yacaaba, the northern headland, is 210 m (690 ft). The harbour is mostly shallow and sandy but contains sufficient deep water to accommodate large vessels. With an area of approximately 134 square kilometres (52 sq mi), Port Stephens is larger than Sydney Harbour.

The port was named by Captain Cook when he passed on 11 May 1770, honouring Sir Philip Stephens, who was Secretary to the Admiralty. Stephens was a personal friend of Cook and had recommended him for command of the voyage. Port Stephens has rather poor soil for the most part, and has limited agricultural potential. For this reason, no large towns developed there historically and it was never developed as a significant port. The major city and port of Newcastle developed at the mouth of the Hunter River, about 45 km (28 mi) south-west of Port Stephens.

The Tomaree Battery on Tomaree Head, was built during 1941 as part of the Newcastle Fixed Defences. The guns at Tomaree afforded protection for Port Stephens, not far from the Newcastle steelworks. The Battery was completed by the end of 1942. It included guns, mortars, rifle pits, a search light station, torpedo tubes and barracks that accommodated the 500 army, navy and air force personnel that served there. The large guns were never fired in anger against the enemy. The same year, a radar station was erected on the summit by the RAAF to detect enemy shipping and monitor flight movements with a 120-kilometre range. Port Stephens is a popular tourism destination with a strong focus on aquatic activities such as whale and dolphin watching, fishing and recreational boating.