Catherine Connolly has been inaugurated as Ireland's 10th President at a ceremony in Dublin Castle.
The ceremony took place in St Patrick's Hall, where all presidents have been inaugurated since 1938. It began with a service of prayer and reflection.
After her inauguration, President Connolly told the audience in St Patrick's Hall that the people have spoken and given their President a powerful mandate, suggesting it is a mandate she intends to use.
She spoke of a republic being a place where everyone is valued, diversity is cherished, and where a home is a fundamental human right.
The President said Ireland is well placed to lead on alternative diplomatic solutions to war, famine and climate change, given our own history, and what she termed Ireland's long and cherished tradition of neutrality and peacekeeping.
She spoke of how she was inspired by the people she met on the campaign trail who toiled without the services and the necessities - something that should no longer exist in a country so wealthy.
Other themes included: making Northern Ireland her first official visit, referencing her desire for national unity through consent; expressing the hope she would have many opportunities to meet our diaspora; and declaring the importance of retaining and growing the Irish language to preserve the soul and spirit of the nation.
Earlier, former president Michael D Higgins received a round of applause as he arrived in St Patrick's Hall for the inauguration ceremony.
Those attending the ceremony included the Taoiseach, the Tánaiste, members of the judiciary, politicians from all parties, along with guests from a cross section of Irish society.
Former Irish presidents Mary McAleese and Mary Robinson were also in attendance.
Ms Connolly was declared the tenth Uachtarán na hÉireann at the ceremony, becoming the third woman to hold the role.
The declaration, as laid out in Bunreacht na hÉireann, was read by Chief Justice Donal O'Donnell and was repeated by Ms Connolly.
She then signed the declaration and was officially declared President of Ireland.
A 21-gun salute was fired from Collins Barracks and Chief Justice O'Donnell handed Ms Connolly the Seal of Office.
Taoiseach congratulates Connolly, pays tribute to Higgins
Addressing the ceremony in Dublin Castle, Taoiseach Micheál Martin offered his "comhghairdeas" to the new President.
The Taoiseach said he has no doubt that President Connolly "will serve our country well".
Mr Martin also thanked former president Michael D Higgins for his "outstanding contribution" in office. He said the country owed him and wife Sabina a "tremendous debt of gratitude".
I stand before you humbly and proudly, says Connolly
"I stand before you humbly and proudly as the tenth president of this beautiful country," President Connolly said.
"The people have spoken and have given their President a powerful mandate to articulate their vision for a new republic, a republic worthy of its name where everyone is valued and diversity is cherished, where sustainable solutions are urgently implemented, and where a home is a fundamental human right," she said.
The President added: "The change that led to this joyful day began with the small group of elected representatives and volunteers facing what appeared to be insurmountable challenges.
"We were led to believe that it was too great a leap, that our ideas were too far out, too left - at odds with the prevailing narrative.
"In shared conversations all over the country, however, it became evident that the dominant narrative did not reflect or represent people's values and concerns.
"Time and time again, people spoke of how it served to silence, to other, to label, to exclude and to stifle critical thinking.
"Along with that meaningful engagement, we saw the emergence of hope. We saw the emergence of joy, along with the courage and determination of people to use their voices to shape a country that we can be proud of," she said.
Ms Connolly's said "our actions today will shape the world our grandchildren will inherit".
She called on people to reflect on the effects of wars and said Ireland has a history of neutrality and peacekeeping and is well-placed to promote alternatives to war.
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Read more:
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President Connolly's first official engagement was a lunch at Áras an Uachtaráin.
The gathering was attended by Government and Opposition leaders along with many invited guests.
Later, she returned to Dublin Castle for a State reception in her honour.
Mr Higgins' term in office expired at midnight on Monday, and he left Áras an Uachtaráin.
He and his wife Sabina were cheered outside the gates of the Áras by the Sanctuary Runners group as they left on Monday evening.
In a statement ahead of the conclusion of his term, Mr Higgins thanked the people of Ireland for the "warmth of reception" given to himself and his wife Sabina over the past 14 years and said that serving as president was "a great privilege".
In the short period leading up to Ms Connolly's inauguration, the presidential duties fell to a commission, comprised up of Chief Justice Donal O'Donnell, Ceann Comhairle Verona Murphy and Cathaoirleach of the Seanad Mark Daly.
