Dun Laoghaire is a suburban coastal town in the traditional county of Dublin in Ireland. It is the county town of Dun Laoghaire-Rathdown, one of the three authorities that replaced the old Dublin County Council.

The town was built following the 1816 legislation that allowed the building of a major port to serve Dublin. It was known as Dunleary until it was renamed Kingstown in honour of King George IV's 1821 visit, and in 1920 was given its present name, the original Irish form of Dunleary. Over time, the town became a residential location, a seaside resort and the terminus of Ireland's first railway.

The harbour, one of the largest in the country, is notable for its two granite piers. The East Pier is particularly popular with walkers, and was featured in the 1996 film Michael Collins, where Liam Neeson (as Collins) and two of his co-stars are seen walking along a seaside promenade, which is actually the Dún Laoghaire East Pier. A band is seen playing on a bandstand in this film scene, and this is the actual bandstand on the East Pier. The bandstand was restored to its original condition in 2010 by the Dún Laoghaire Harbour Company.

It took 42 years to construct the harbour, from 1817 to 1859. The obelisk near the old ferry port terminal at the harbour commemorates the construction of this harbour.

A lighthouse was at the end of the East Pier, while the new headquarters of the Commissioners of Irish Lights (the General Lighthouse Authority for Ireland) is on Harbour Road.

South of the harbour is Scotsman's Bay, where there was a Victorian seaside amusement area, with walks, shelters and baths. The walks and shelters are largely intact. Dún Laoghaire Baths have been derelict for many years, but were repainted in bright colours in 2012. Plans for restoration of this area are much debated, and some of the more ambitious ideas have been highly controversial.

A traditional Victorian-style park, the People's Park, is at the eastern end of George's Street, and including still-functioning tea rooms.

At least one traditional "cabman's shelter" survives - these were small buildings built for the drivers of horse-drawn taxis.

Community facilities include the Boylan Community Centre, the Dún Laoghaire Scout Den, and a community information service in the tower building of St Michael's Church.

A large modern library headquarters was built by the harbour in recent years.