MUSICLollapaloozaAdd TopicLollapalooza 2021: See Megan Thee Stallion, Post Malone, Machine Gun Kelly, more perform Hannah YasharoffUSA TODAYLollapalooza is back.After the 2020 Chicago music festival was canceled by the coronavirus pandemic, the four-day event returned July 29 through Aug. 1, 2021. Roughly 100,000 attendees were expected each day, all of whom were required to show proof that they've been vaccinated for COVID-19or tested negative within the last three days.Scroll through for photos of all your favorite stars performing, including Megan Thee Stallion, Post Malone, Machine Gun Kelly, Princess Nokia, Modest Mouse and more.Amy Harris/Invision/APYoung Thug stands onstage during a closing performance on Day 4 of Lollapalooza.Gary Miller, FilmMagicRico NastyAmy Harris, Amy Harris/Invision/APBrittany HowardTimothy Hiatt, WireImageSarah BarriosTimothy Hiatt, WireImageBrian Sella of The Front BottomsTimothy Hiatt, WireImageBen Bridwell, lead singer of Band of HorsesRob Grabowski, Rob Grabowski/Invision/APModest MouseAmy Harris, Amy Harris/Invision/APRussell Higbee of Modest MouseRob Grabowski, Rob Grabowski/Invision/APIsaac Brock of Modest MouseRob Grabowski, Rob Grabowski/Invision/APSofia ValdesAmy Harris, Amy Harris/Invision/APPrincess NokiaAmy Harris, Amy Harris/Invision/APDermot KennedyAmy Harris, Amy Harris/Invision/APMegan Thee Stallion took the stage on Day 3 of Lollapalooza.Rob Grabowski/Invision/APMachine Gun Kelly performs a surprise setGary Miller, FilmMagic… and girlfriend Megan Fox was spotted in the crowd.Gary Miller, FilmMagicPost MaloneRob Grabowski/Invision/APTate McRaeTimothy Hiatt, WireImageJourney, from left: Arnel Pineda, Marco Mendoza, Jonathan Cain and Neal Schon.Rob Grabowski/Invision/APBIATimothy Hiatt, WireImageTrippie ReddAmy Harris/Invision/APSameer Gadhia of Young the GiantRob Grabowski/Invision/APJason Singer of MichiganderRob Grabowski/Invision/APMichelle Joy of CannonsAmy Harris/Invision/APJac RossAmy Harris/Invision/APRoddy Ricch performs on Day 2 of Lollapalooza.Rob Grabowski/Invision/APJack HarlowRob Grabowski/Invision/APLauvAmy Harris/Invision/APSa-RocAmy Harris/Invision/APPolo G performs on day two of the Lollapalooza Music Festival on Friday, July 30, 2021, at Grant Park in Chicago. (Photo by Amy Harris/Invision/AP) ORG XMIT: ILRP127Amy Harris/Invision/APJake Wesley RogersAmy Harris/Invision/APTobi LouRob Grabowski/Invision/APJordan Benjamin of GrandsonRob Grabowski/Invision/APKim Petras, left, and Steve Aoki pose on Day 1 of Lollapalooza.Amy Harris/Invision/APPlayboi CartiRob Grabowski/Invision/APFlo MilliRob Grabowski/Invision/APAlly Michalka and AJ Michalka of Aly & AJ.Amy Harris/Invision/APSAINt JHNAmy Harris/Invision/APOlivia O'BrienTimothy Hiatt, WireImageEric Burton and Adrian Quesada of Black PumasAmy Harris/Invision/APLPAmy Harris/Invision/APMaxAmy Harris/Invision/APOrville PeckRob Grabowski/Invision/APGuests arrive for the first day of the Lollapalooza.Scott Olson, Getty ImagesGuests are asked to show proof they've been vaccinated against the COVID-19 virus.Scott Olson, Getty ImagesFeatured Weekly Ad