Twelve people have been arrested and a number of drug seizures made at the Oxegen music festival in Punchestown.
The three-day event gets under way today, but revellers began the journey to the Co Kildare venue yesterday when camp sites opened.
Gardaí said the arrests were for public order and drug possession offences.
Up to 80,000 people are expected to attend the music event.
Gardaí said up to 18,000 people travelled to Punchestown yesterday by bus, with the remainder arriving by car.
A traffic management plan put in place to deal with the thousands of concertgoers went "very well", a Garda spokesman said, and local gardaí have urged people attending the site to follow the signs and directions of gardaí and stewards.
A free park and ride facility is in place at Goffs, Kill, Co Kildare, with shuttle buses transporting people to and from Punchestown Racecourse.