Thousands of people are expected to turn out for St Patrick's Day events all over the country today - with events also taking place around the world.
More than 150 parades are taking place across Ireland.
Traffic restrictions are in place on most parade routes and people, are advised to plan their route before travelling.
President Michael D Higgins will attend the Dublin parade, which gets under way at noon.
The parade begins at Parnell Square, and will travel through the city before finishing up at Kevin Street.
Game Of Thrones star Liam Cunningham is Grand Marshall for the parade, and called it a 'huge honour'.
He observed: "I've been to the parade many times... 50 years ago when I was young and attractive, and my three kids have been up on my shoulders in hail, rain or snow.
"To be asked to do this... it's one of the most gratifying requests I've ever had. I'm delighted to be part of it."
Star Wars actor Mark Hamill will be the inaugural international guest of honour at the parade, and will watch festivities from the Presidential stand.
Let me shout it from the rooftops: BEANNACHT DE LA FEILE PADRAIG!!! https://t.co/cSUJRBCfqW— Mark Hamill (@HamillHimself) March 17, 2018
Parades are also taking place in cities, towns and villages across the country.
Tens of thousands are expected at the parades in Cork, Waterford and Galway, while smaller towns will also boast their own parade themes - in Sligo, for example, the focus will be on “The Year of the Woman” to mark the 100-year anniversary of women’s right to vote.
However, those attending the parades are being warned of potentially cold weather - with Met Éireann having issued a status yellow snow-ice warning for the entire country, which comes into effect from midday.
Government ministers have travelled to different locations around the world to mark St Patrick's Day.
The Taoiseach is in New York City, where he will march in the annual Fifth Avenue parade.
Tourism Ireland, meanwhile, says around 290 iconic landmarks in 48 countries around the world will be illuminated in green over the weekend.
It comes as part of their annual Global Greening campaign to celebrate the island of Ireland and St Patrick.