The new Garda Síochána commissioner has said protecting the Irish state from the threat of terrorism will continue to be a priority for the police force.
Speaking as he was sworn in, Drew Harris said that had "saved lives and protected communities on both sides of the border".
The ceremony took place in Dublin early on Monday, when he signed an oath.
Mr Harris, 53, is an ex-Police Service of Northern Ireland deputy chief constable.
His appointment was announced in June. It is the first time the job has been given to an external candidate.
Speaking after he was sworn in, Mr Harris said: "I know at first hand the commitment, dedication and sacrifice that has been made by members of An Garda Síochána in securing the state, particularly from the threat of terrorism.
"This has saved lives and protected communities on both sides of the border.
"That work must and will continue to be a priority for the organisation and me as commissioner."
His appointment is for a five-year term and he will receive an annual salary of 250,000 Euros (£200,300).
On Sunday, Irish Justice Minister Charlie Flanagan defended the new Garda commissioner, saying Mr Harris was "noted very much for impartial policing".
At his swearing-in ceremony, Mr Harris said he would be focused on "protecting the people of Ireland and in particular the vulnerable within our society".
He added that the Garda would be transparent and open to concerns raised both internally and externally.
"Where I envisage the organisation now going is towards accountable policing with openness and integrity," he said.
Josephine Feehily, the chair of the Policing Authority, said she did not have any concerns about Mr Harris dealing with intelligence and security issues.