Millions of revellers are preparing to celebrate St Patrick's Day at home and abroad.
In Dublin, the parade will wind from Parnell Square, along O’Connell Street and Dame Street to St Patrick’s Cathedral, starting at 12 noon.
The theme for this year’s parade is a scientific one: 'How? What? Why?' which is inspired by Dublin’s standing as the 2012 City of Science.
Floats and costumes are based on scientific concepts and questions, posed by schoolchildren, such as: How is electricity made? How is a rainbow formed? What makes the weather change?
Last year’s event attracted around 550,000 spectators but festival organisers expect an even larger turnout today.
Veteran soccer commentator John Giles will lead the parade as Grand Marshal when it kicks off at midday.
President Michael D Higgins will enjoy his first St Patrick’s Day as head of state when he takes part as special guest at the GPO in O’Connell Street.
Belfast will have a carnival and parade throughout the city centre with street performers and a free music concert at Custom House Square.
With an Irish diaspora of around 70 million, major cities across the globe will also hold their green-inspired galas.
Dublin city centre will be a hive of activity with St Stephen’s Green and Temple Bar’s Meeting House Square serving up traditional Irish music performances, while Merrion Square is expected to attract youngsters with a Ferris wheel and other funfair attractions.
Around 240,000 passengers are expected through Dublin Airport over the bank holiday weekend. Both terminals will be decked with balloons and bunting to welcome visitors and jugglers, stiltwalkers, bands and schoolchildren will give the travellers a taste of the roaring revelry they can expect over the weekend.
Animals are also expected to join the celebrations as Dublin Zoo undergoes a green makeover, while zookeepers host St Patrick’s-themed talks. Even animals across the water are getting in on the action, with a flock of sheep in West Lothian, Scotland boasting freshly dyed green wool.
The Prince’s Palace in Monaco and the Sydney Opera House will be lit up in honour of St Patrick, as will Niagara Falls, the Leaning Tower of Pisa and the Burj al Arab hotel in Dubai.
Taoiseach Enda Kenny will promote Ireland to leaders in business, politics and tourism in the US when he takes in the sights and sounds of Indiana.
Mr Kenny will then travel to New York on Monday for Ireland Day, where he will ring the bell of the New York Stock Exchange and then will jet to Washington on Tuesday for a St Patrick’s party with US President Barack Obama.
The Taoiseach has urged the nation to celebrate St Patrick’s Day with pride, saying that being Irish is a badge of honour.
“St Patrick’s Day is a day when the world goes green and people look to this little island in the north Atlantic with admiration and pride,” said Mr Kenny in a message for March 17.
“It is a chance to celebrate everything it really means to be Irish. We should never lose sight of the fact that despite these difficult economic times, that we have a unique heritage, a culture and a history to really be proud of.”