More than 2,000 flights will arrive at and depart from the Republic's three main airports this bank holiday weekend, in the busiest period ever for Aer Rianta.
It will also be busy on the roads with Bus Éireann warning passengers to expect delays of more than an hour on many routes from midday today.
Bus Éireann expects to carry more than 100,000 passengers on its Expressway and provincial services between today and next Tuesday.
Normal weekday timetables will operate today and tomorrow. On Sunday and Monday normal Sunday timetables apply, with some cancellations.
The company has warned that because of expected delays on Friday and Monday, commuters should travel as early as possible and allow for additional time if making connections to their final destination.
Bus Éireann has also said it will run a special bus service from Dublin to the Naas races on Monday. The service will depart from Busáras 90 minutes before the first race at 2.25 p.m.
Iarnród Éireann will put on additional services for those attending the All-Ireland football and hurling championship fixtures in Dublin and Thurles.
On Saturday, Clare play Kilkenny in the All-Ireland hurling semi-final replay in Thurles. Extra carriages will be put on the 1.30 p.m. regular service from Ennis to Thurles. An extra return service run from 6.20 p.m. will be deferred until 6.45 p.m. if the match runs in to overtime.
A special service for Roscommon fans travelling to see their county take on Dublin in Croke Park on Sunday in the football championship qualifiers will leave Claremorris at 9.20 a.m. It will depart Dublin's Heuston station after the game at 6.20 p.m.
More than 375,000 passengers will travel through Dublin, Shannon and Cork airports over the weekend, an increase of around 6 per cent on last year. More than 2,000 planes will use the airports, including 320 charter flights.
Passengers are reminded to check in 90 minutes before their flights are due to depart, and to remove sharp objects from their hand luggage.
Meanwhile, thousands of people will be attending festivals and events all over the country during the weekend.
In Waterford the Spraoi street party runs from today until Sunday night. It features street performers from all over the world, including Morris dancers, the explosive Bruce Airhead and a troupe of African singers.
The closing State of the Art parade is inspired by the looting in Baghdad last year when priceless artefacts were stolen and destroyed.
It features an angry mob burning and slashing its way through civilisation, and ends in a spectacular firework display.
The Commitments open the Mitchelstown Music Festival in Co Cork tonight with a free concert in the New Square. Disco legends Kool and the Gang complete an eclectic line-up on Sunday evening.
Cork city will feature the Cork Gay Pride festival.
The Le Chéile festival takes place in Oldcastle, Co Meath, where performers will include Shane MacGowan and the Popes, Mundy, Des Bishop and Mary Coughlan.
Poet and professor Brendan Kennelly will open the Sligo Festival of the Arts in the Hawk's Well theatre at the weekend. The theatre will also be hosting the Abbey's touring production of The Playboy of the Western World on Saturday at 8.30 p.m.
In Dublin the Lambert Puppet Theatre will be performing Oscar Wilde's The Selfish Giant at 3.30 p.m. on Saturday and Sunday at their Monkstown venue.