Lollapalooza's three-day event kicked off its 20th anniversary bash on Friday at Chicago's Grant Park. The trend-setting music festival was established by Jane's Addiction's Perry Farrell and has been held annually at Grant Park since 2005.
Big bands headlining Friday included Foster the People and Cults, Muse and Coldplay -- who warmed up the crowd with a surprising performance of Jay-Z's "99 Problems," inspiring thousands to get up and dance.
"All three days are sold out, 90,000 a day," Farrell said to USA Today. "Lollapalooza is such a beautiful, exciting notion now. All our ideas are so much bigger and grander."
To check out the full list of bands, rappers, pop stars, soul singers and DJs -- click here.