In Northern Ireland, former enemies on opposite sides of the political spectrum launched a new power-sharing government. The agreement brings together hard-line Unionists who want Northern Ireland to continue to be part of Britain, and hard-line Republicans, who support a united Ireland.
Years of effort by the British and Irish prime ministers led to the ceremony, aimed at bringing an end to decades of violence between Protestants and Roman Catholics.
Communities are still divided in Northern Ireland, and some have called the recent peace simply the peace of exhaustion. But both sides have, at least for now, agreed to resolve issues politically and not through violence.
Protestant cleric Ian Paisley and Martin McGuinness of the Irish Republican Army's political ally, Sinn Fein, were sworn in as first minister and deputy minister, respectively, of the new government.
Paisley called it a special day and a new beginning. McGuinness called it one of the mightiest leaps forward this process has ever seen. British Prime Minister Tony Blair and Irish leader Bertie Ahern, who have both guided and encouraged the peace process, were in Northern Ireland for the swearing-in ceremony.
In Northern Ireland, previous efforts toward power-sharing agreements between more moderate politicians have failed. But there is greater hope this time, as the extreme wings of both sides, represented by Paisley and McGuinness, have signed onto it.
And now, with the ceremonies over, comes the equally difficult business of cooperating in the day-to-day running of local affairs in Northern Ireland.