Latitude Festival at Henham Park near Southwold is celebrating its tenth anniversary.
35,000 people are expected to attend on each day over Friday and the weekend.
This year people will also be allowed to swim in the lake for the first time.
Headliners include Alt J, Portishead, James Blake and the Manic Street Preachers.
Marketing manager Jen Roberts said: "We've got something for everyone. It's bigger and better every year.
"This is our tenth edition so it's going to be a good one and the weather just looks blissful."
Latitude styles itself as Britain's largest multi-arts festival with a Literary Arena, poetry, comedy, dance, films as well as the music.
Traffic congestion is likely during the weekend around the festival site which is bordered by the A12 and the A145 north of Blythburgh.