A minute's silence has been held across Europe in memory of the victims of the Paris attacks.
A total of 129 people died in the attacks on bars and restaurants, a concert hall and the Stade de France.
French President Francois Hollande was at the Sorbonne University in Paris surrounded by his cabinet to mark the occasion.
Hundreds of people gathered at the central Place de la Republique, near the site of many of the attacks on Friday.
Big crowd now at Place de La Republique for Minute of Silence. pic.twitter.com/ovocgyoOcB— Robert Shortt (@RobertShortt) November 16, 2015
Flags were lowered on State buildings across Ireland as a mark of respect for the victims.
President Michael D Higgins and his wife Sabina signed a book of condolences at the French Embassy on Merrion Square in Dublin after attending the minute's silence.
Mr Higgins said he was passing on the sympathies of the Irish people and also conveying a message of tolerance.
He was greeted by French Ambassador Jean-Pierre Thébault who led one minute's silence at 11am.
Mr Thébault told the crowd gathered that they had lost some of their family but he said they say no to terrorism and yes to freedom.
Dr Muhammad Umar Al-Qadri, Al-Mustafa Islamic Centre mtg French ambassador and placing wreath at French Embassy pic.twitter.com/wfEAnQjeNK— Sandra Hurley (@sandra_hurley) November 16, 2015
Dr Umar Al-Qadri, Imam of the Islamic Cultural Centre, laid a wreath at the embassy and said the terrorists were trying to divide communities and he said they were criminals.
The crowd gathered outside the embassy sang the French national anthem before breaking out in applause after the minute's silence.
Minister for Foreign Affairs Charlie Flanagan has conveyed the condolences of the Irish people to the French Secretary of State for European Affairs Harlem Desir in Brussels.
A minute's silence was observed at the European Union Foreign Affairs Council.
A candlelit vigil, organised by some of the French residents who live in the city and county, is to be held in Cork City centre later today. It will take place at 5.30pm at the National Monument.
Earlier, a minute's silence was observed at several locations in the city including on campus at UCC, at the Tyndall Institute and at the Cork Institute of Technology, where a vigil of solidarity will be held at lunchtime tomorrow.
Some of the 214 French students studying at CIT were among the first to sign the book of condolence opened there.
Both international and Irish students and staff at CIT were also alerted by text about the college's counselling and medical services should they need assistance.
Flags are at half mast at many of the city's public buildings.
At midday, the Lord Mayor of Cork Councillor Chris O'Leary was joined by the city's Honorary French consul Patricia Mallon to sign a book of condolence, which has been opened by him at Cork's City Hall.
Elsewhere, silence descended across Northern Ireland as people paused to reflect on the horrific events in Paris.
At Stormont, politicians from all sides stood together in Parliament Buildings to pay tribute to the victims.
Northern Ireland Secretary Theresa Villiers stood with First Minister Peter Robinson and Deputy First Minister Martin McGuinness.
Public museums and other cultural venues in the Paris area reopened this afternoon, three days after the terror attacks, the culture ministry said.
The museums would reopen at 1pm local time, the ministry said in a statement.
Cinemas were also ordered to close following the attacks but most of them reopened yesterday after a 24-hour closure.
Large crowd applauding after one minutes silence. pic.twitter.com/bkpfWfn7c1— Sandra Hurley (@sandra_hurley) November 16, 2015
Schools, sports venues and parks will also reopen today, along with street markets, which will be under "special scrutiny", the Paris town hall said in a statement.
Meanwhile, the Department of Foreign Affairs has said it is continuing to offer support to the family of the Irishman who was injured in the Paris attacks.
The man is said to be in a stable condition in hospital.