Tens of thousands of people have taken to the streets to mark the occasion...
Hundreds of thousands of people across Ireland have taken to the streets to watch the annual St Patrick's Day parades.
The largest parade took place in Dublin, with huge crowds lining the capital's streets despite very cold temperatures.
Game Of Thrones star Liam Cunningham was Grand Marshall for the parade, while Star Wars actor Mark Hamill was the inaugural international guest of honour at the parade.
Participants ranged from locals celebrating 100 years since women were allowed to vote, to marching bands from across the world.
Huge crowds have also gathered in Limerick for the parade through the city:
Other cities around the country also saw all manner of costumed marchers and elaborate floats.
The creative brilliance of @BeatCarnival once again supporting Belfast’s St Patrick’s Day parade with representation from all parts of the city. Important for civic unionism to play their part. pic.twitter.com/excA4DTyHu— john kyle (@cllrjohnkyle) March 17, 2018
#corkcc where would the Cork #StPatricksDay2018 parade be without the Cork Barrack Street band, large numbers out in force this cold afternoon; over 180 years entertaining the Cork masses! @corkcitycouncil pic.twitter.com/CelMqKo4nu— Kieran McCarthy (@cllrkmac) March 17, 2018
It isn't just Ireland, of course, with parades also taking place around the country to mark the day.
The Taoiseach was among those marching in New York, while there were also events held everywhere from Oslo to Macau: