MANCHESTER, Tenn., June 18 — Radiohead was a dance band when it headlined the Bonnaroo Music & Arts Festival here on Saturday night. Tom Petty and the Heartbreakers were a dance band. Clap Your Hands Say Yeah, the pride of indie-rock, was a dance band. Ricky Skaggs and his bluegrass band Kentucky Thunder were a dance band. If the Juilliard String Quartet had performed at Bonnaroo, it would have been a dance band too. Standing in the 700-acre pasture in Tennessee that has been Bonnaroo’s home since it started in 2001, fans get physical with music presented in happy excess.

Bonnaroo started as a festival of jam bands: fast-fingered, long-playing, perpetually touring groups that would rather have a good time than act cool and hip. The tie-dyed trappings and collegiate dreadlocks of jam-band followers invite mockery, but behind them is at least some remnant of 1960’s utopianism. Jam bands often refer fans back to their sources — in blues, jazz, country, funk, reggae, world music — and Bonnaroo books a broad assortment. The first Bonnaroo sold 70,000 tickets without advertising; after growing to 90,000 in 2004, the festival put a cap on its capacity at 80,000 and was sold out this year.

But there was change at the top of the bill. Radiohead and Mr. Petty, two of the three headliners — those who play long prime-time sets without four other stages of competition — aren’t known as jam bands, though Mr. Petty drew an affirmative roar when he asked the audience, “Can I jam for you?” He did. In “Refugee” the Heartbreakers’ guitarist, Mike Campbell, switched his tone and technique to emulate Jerry Garcia of the Grateful Dead, the jam-band patriarchs. Over the last five years jam bands have receded slightly. The Dave Matthews Band, a past draw at Bonnaroo, still jams its way across the arena and stadium circuit. But the Grateful Dead fragmented after Garcia’s death in 1995, with the survivors occasionally gathering as the Dead (who headlined Bonnaroo in 2004) and many spinoffs. One spinoff, Phil Lesh and Friends, was Sunday night’s scheduled finale this year.

Phish, once an arena staple, disbanded in 2004. Two of its members — the guitarist Trey Anastasio and the bassist Mike Gordon — performed separately and together this weekend. At Superjam in the wee hours of Sunday morning, Mr. Anastasio and Mr. Gordon unveiled new songs they had written together. “I see you coming back again,” they sang in the anthemic “Seasons.” Was it a reunion tease?

Jam-circuit regulars like Moe, Umphrey’s McGee, Robert Randolph, the Disco Biscuits, and Medeski Martin and Wood were here this year. Oysterhead — the trio of Mr. Anastasio, Primus’s bassist Les Claypool and the Police’s drummer, Stewart Copeland — regrouped to play songs that are basically funk vamps with cackling, sometimes obliquely political lyrics from Mr. Claypool.

But listeners impatient with jam-band noodling had other choices. My Morning Jacket, in a midnight set on Friday night, left behind the electronic experiments of its most recent album, “Z,” and unleashed its three guitars in songs that pealed and surged in structures with monumental architecture. Then it turned to other bands’ material, including the Who’s mini-opera “A Quick One While He’s Away.”

There was leathery, impassioned soul from Bettye LaVette and a surprisingly extroverted set by Cat Power with her Memphis Rhythm Band. Bright Eyes played Conor Oberst’s confessional, self-conscious songs as a mixture of melodrama and hoedown. Buddy Guy teased and streaked through his blues.

A Saturday-afternoon set by Beck had a comic veneer — lip-syncing marionettes behind the band — that didn’t mask the somber thoughts of love and death in his songs. Damian Jr. Gong Marley, one of Bob Marley’s sons, didn’t just follow his father’s style. He not only sang but also toasted, or rapped, in the dancehall style that dominates current reggae. He also asked, “Do you like Bob Marley?” and then played Marley songs (like “Bad Card” and “Zimbabwe”) that many had apparently never heard.

There was an all-star New Orleans contingent at the festival: the idealistic funk of the Neville Brothers, the Preservation Hall Jazz Band and the alliance of Elvis Costello and the New Orleans songwriter Allen Toussaint, whose piano and Crescent City Horns carry Mr. Costello’s songs south. Their fierce mambo-funk arrangement of “Bedlam” may be the first time New Orleans horns have tangled with a theremin. Dr. John gave Bonnaroo’s neo-hippies a glimpse of vintage psychedelia when he appeared in full Night Tripper regalia — feathered headdress, fur-trimmed cape — with songs from his voodoo-steeped 1968 album “Gris-Gris.”

And of course there was Radiohead, playing a magnificent set. Its songs were bleak, complex and filled with tensions: lush melody attacked by noise, rhythm pulling against rhythm, a lone guitar suddenly caught up in crescendos like earthquakes. Yet Thom Yorke was dancing across the stage as he sang, twirling and twitching and jittering, making his own kind of Bonnaroo groove. Not like a hippie, but not painfully hip either.