Dun Laoghaire is the administrative centre of Dun Laoghaire-Rathdown county in the Republic of Ireland. It is located 12 km to the south-east of the City of Dublin.

The town has a population of around 180,000. Administratively, it is within the Dun Laoghaire-Rathdown County which covers approximately 127.31 sq kms.

There is a ferry port at D?n Laoghaire which has crossings to and from Holyhead in Anglesey, North Wales; this is a popular route for tourists travelling across the Irish Sea from Britain. With the advent of faster boats, day trips have become more popular using the D?n Laoghaire port. The harbour is notable for its two granite piers, especially the East Pier which is popular with walkers. The area to the north of West Pier is used all year round by wind surfers as a launch point. The 500 berth marina, opened in 2001, is the largest in the country, and there are five yacht clubs. Other attractions include the National Maritime Museum of Ireland and a Martello tower in nearby Sandycove, known as the James Joyce Tower. D?n Laoghaire Institute of Art, Design and Technology is also situated here. The town provides excellent shopping and has plenty of restaurants, pubs and clubs. It lies just 7 miles from Dublin city and 16 miles from Dublin airport.

The town was founded by Laoghaire, a 5th century King of Ireland who used the site as a base to carry out sea raids on Britain and France. He built a great stone fort, or 'dun' in the centre of the town, but this was demolished in 1803 to make way for the building of a Martello tower. The building of the harbour began in 1817; it was intended as a place of refuge where large ships could berth in safety away from the Irish Sea. However, the harbour was widened, leading to silt washing in, making it impossible for the larger ships to enter, although the Mailboat still operated, carrying mail, cargo and passengers. Soon a thriving port, a railway link was built to Dublin, which was the first railway in Ireland, and the town changed from a small fishing village into a prosperous seaside town. Today, the town provides excellent shopping and has plenty of restaurants, pubs and clubs.

Economically, at one time cattle, lead ore, and granite were exported and coal, iron, timber, corn, and foodstuffs were imported. The city is now a resort and yachting and fishing centre, and the harbour is used for cross-channel passenger, mail, and car ferry services.

The name derives from the founder of the town, Laoghaire, a 5th century King of Ireland who used the site as a base to carry out sea raids on Britain and France. Dun is an Irish word meaning fort. The town was renamed Kingstown in honour of a visit by King George IV in 1821, but reverted to its ancient Irish name in 1921 by a resolution of the town council. Dun is an Irish word meaning fort.