Lollapalooza (Lolla) is an annual American four-day music festival held in Grant Park in Chicago. It originally started as a touring event in 1991, but several years later, Chicago became its permanent location. Music genres include but are not limited to alternative rock, heavy metal, punk rock, hip hop, and electronic dance music. Lollapalooza has also featured visual arts, nonprofit organizations, and political organizations. The festival, held in Grant Park, hosts an estimated 400,000 people each July and sells out annually. Lollapalooza is one of the largest and most iconic music festivals in the world and one of the longest-running in the United States.

Lollapalooza was conceived and created in 1991 as a farewell tour by Perry Farrell, singer of the group Jane's Addiction. The first Lollapalooza tour had a diverse collection of bands and was a commercial success. It stopped in more than twenty cities in North America. In 2020, Spin rated the first Lollapalooza as the best concert on a list of "The 35 Greatest Concerts of the Last 35 Years". Lollapalooza then ran annually until 1997, and was revived in 2003. From its inception through 1997 and its revival in 2003, the festival toured North America. In 2004, the organizers decided to expand the dates to two days per city, but poor ticket sales forced the 2004 tour to be canceled.

In 2005, Farrell and the William Morris Agency partnered with Austin, Texas–based company Capital Sports Entertainment (now C3 Presents) and retooled the event into its current format as an annual festival in Chicago. In 2014, Live Nation Entertainment bought a controlling interest in C3 Presents.

In 2010, it was announced that Lollapalooza would remain in Chicago, while also debuting outside the United States, with a branch of the festival staged in Santiago, Chile on April 2–3, 2011, where it partnered with Santiago-based company Lotus. In 2011, Geo Events confirmed the Brazilian version of the event, which was held at the Jockey Club in São Paulo on April 7–8, 2012. The Argentine version started in April 2014 in Buenos Aires and in November 2014, the first European Lollapalooza was announced, and was held at the former Berlin Tempelhof Airport.