There are over 120 parades taking place across the country today with the largest being in the capital.
Almost 500,000 people are expected to line the streets which has resulted in a host of traffic restrictions, road closures and changes to public transport timetables.
Here's everything you need to know:
A Sunday timetable will operate on all routes today while City Tours, Coastal Tours and Ghostbus will not operate.
A full Nitelink service will operate tonight but there will be no Nitelink service on Monday.
Due to parades across Dublin - as well as Kildare - Dublin Bus routes may take a different journey than usual so that's something to look out for.
— Trinity College Dublin (@tcddublin) 17 March 2019
Normal Sunday service with a number of cancellations and additional services.
Normal Sunday service is running with some exceptions.
Green Line trams will only run from Brides Glen to St. Stephen’s Green and from Broombridge to Dominick until 6pm.
Red Line services from Saggart/Tallaght will terminate at Smithfield until around 3pm.
Normal Sunday service, though Tara St station in Dublin will not open until 4pm.
DUBLIN CITY CENTRE PARADE
The country's marquee parade gets underway at midday, beginning at Parnell Square, working its way through the city before finishing on Cuffe St.
The following roads will be closed throughout the day:
- Kevin St Upper/Lower
- Cuffe Street
- St Stephen’s Green South
- Mountjoy Street
- Mountjoy Street Middle
- Palmerstown Place
- O’Connell St Upper and Lower
- O’Connell Bridge
- Westmoreland Street
- College Green
- Dame Street
- Lord Edward Street
- Christchurch Place
- Nicholas Street
- Patrick Street
- New Street South,
- Clanbrassil St Lower
- Wellington Street
- St Mary’s Place North
- Granby Row
- Parnell Square North
- Parnell Square East
- Cavendish Row
Enjoy your St. Patrick's Day 2019, hopefully more than this man.....
— Darren Cleary (@RadioCleary) 17 March 2019