About 15,000 people took part in millennium celebrations in Derry, where a huge fireworks display lit up the River Foyle. Revellers, including John Hume, watched a 2,000-strong choir - drawn from all over the city - perform on the city's historic walls.
The choir sang a new arrangement of Danny Boy. Mr Hume said it was an emotional occasion. "It was very poignant and beautiful. It was an extremely simple idea but a great one. Everybody really enjoyed it.
"It was an appropriate time to stop for a moment and think about all the people who were robbed of the opportunity to see the new millennium and also to look forward to a better future for our entire society."
The song was broadcast around the world by satellite so Derry exiles could hear it. Later, people gathered for the Circle of Light, a procession around the city walls which culminated in a huge fireworks display at midnight.
Living Our Lives was the theme of Derry's 2000 celebrations. The crowds in Guildhall Square were entertained by a series of local bands. "We are really looking forward to the new millennium in Derry," said Emmett Doherty. "This city has a great future."
A woman was rescued by firefighters after climbing onto scaffolding at the Guildhall. Four people were arrested following minor incidents, but there was no serious trouble and nobody was injured.
In Omagh, Co Tyrone, where 29 people were killed by the "Real IRA" car-bomb 18 months ago, there was an interdenominational prayer service. In Downpatrick, Co Down, there was a cross-community Christian service in Market Street.
At Newtownstewart, Co Tyrone, Catholics and Protestants greeted each other after attending religious services at churches on different sides of Main Street. A beacon was ignited on Slemish Mountain in Ballymena, Co Antrim, where St Patrick is reputed to have tended sheep in AD 400.
A symbolic bridge of light was organised to link the communities on both sides of the Border at Carlingford Lough above Rostrevor, Co Down.
In Craigavon, Co Armagh, about 20,000 people gathered at the watersports centre on Lough Neagh for a fireworks display. A glowing dragon boat formed part of the celebrations.
