Annalong (from Irish Áth na Long, meaning 'ford of the ships') is a seaside village in County Down, Northern Ireland. It is at the foot of the Mourne Mountains, 8 miles (13 km) south of Newcastle. Annalong is in the civil parish of Kilkeel, the barony of Mourne, and the Newry and Mourne District Council area. It had a population of 2,037 at the 2021 census. The village formerly exported dressed granite and is now a fishing and holiday resort.

In the census report of 1659, Annalong is referred to as a 'quarter' - a sub-division of a townland - in this case Moneydarraghmore. Like practically every locality in Mourne, the name derives from the Irish Celtic (Gaelic) - Ath na Long. This means 'the ford of the ships' - a reference to some crossing on the river near where it enters the harbour. It likely relates to around a thousand years ago when the Viking longships found some shelter at the mouth of the river. There is no material evidence of the Vikings ever having settled here. However, there are some words in the local dialect which would appear to suggest Norse influence, such as; 'selk', the local name for the common seal; to 'set allow' is to set on fire; to 'hain' is to eke out; 'holm' refers to low-lying land close to the river.

On 13 January 1843, fishing boats from Newcastle and Annalong set out for the usual fishing stations but were caught in a gale. Fourteen boats were lost in the heavy seas, including a boat that had come to the rescue. Only two boats survived, the Victoria and the Brothers. In all, 76 men perished, 30 of them from Annalong.

It is estimated that around 250 men from Annalong served in the Great War (1914–1918). These men were all volunteers, as conscription was only applied to Great Britain, not Ireland.

Annalong Cornmill was built in the 19th century and operated until the 1960s, and was one of the last working watermills in Northern Ireland. It contains a grain drying kiln and three pairs of millstones. It is powered by a 15 ft water wheel and a 1920s Marshall "hot-bulb" 20hp engine. Restoration began in 1983 after it was acquired by Newry and Mourne District Council, and it reopened in 1985.

Annalong Harbour was enlarged in the 1880s to cope with the increased granite exports. A purpose-built standard gauge railway was built to transport almost all of the material for the construction of the reservoir.

Annalong Holiday Park is a caravan park owned by Chestnutt Holiday Parks located in the centre of the village. Moneydarragh Hub is a social centre offering classes, well-being and business collaboration.

Annalong Coastguard Station has a long history tied to maritime safety and smuggling prevention along the Mourne coast.