PROVIDENCE, R.I. — Tickets for the main two days of this year’s Newport Folk Festival sold out five months early and before anyone knew who was playing — another indication of how the 54-year-old event is staying fresh and relevant with a mix of musical icons and young artists looking for their big break.

The festival, which runs today through Sunday, began in 1959 with performances from Joan Baez and Pete Seeger. It was expanded this year to three days of performances by more than 50 acts on four stages.

While this year’s lineup features big names like Ramblin’ Jack Elliott, Beck, Feist and the Lumineers, it also boasts dozens of lesser-known bands from myriad genres nationwide. Most of the artists reflect a surge in popularity for music that eschews technological pop prowess in favor of acoustic instruments, unadorned vocals and themes as reminiscent of the 19th century as they are of today.

“I think it’s authenticity,” said festival producer Jay Sweet. “It’s not the biggest festival. We don’t have any frills. There’s no cool light show, no dancers. For us, it’s all about the music, creating music that’s built to last, built to be part of a tradition.”

The festival gets underway Friday at its longtime home at Fort Adams State Park, a historic coastal fortification that boasts commanding views of sailboats plying the tranquil waters of Narragansett Bay. Its sister festival, the Newport Jazz Festival, is scheduled for the following weekend.

The Folk Festival is arguably enjoying its best years since the folk heydays of the 1960s, when Baez, Seeger and Johnny Cash all played Newport and where Bob Dylan angered folk fans and changed American music forever by going electric in 1965.

Two years ago, the festival sold out in advance for the first time ever. Last year, tickets were gone three months in advance. This year, they were gone before organizers even released the lineup.

Artists interviewed by The Associated Press credit festival organizers, and a resurgence in interest in roots music, an umbrella term that encompasses folk, stripped-down country, blues, bluegrass, gospel and other genres from the American songbook. It’s a trend pushed by bands like Mumford and Sons and the Lumineers, who play Newport on Sunday.

“It’s a folk festival, but they’ve opened the gates to a big variety of people,” said Nicki Bluhm of Nicki Bluhm and the Gramblers, a California-based band playing its first Newport gig. “What’s appealing to people right now is real music played by real people.”