The Altamont Speedway Free Festival was a counterculture rock concert in the United States, held on Saturday, December 6, 1969, at the Altamont Speedway outside of Tracy, California. Approximately 300,000 attended the concert, with some anticipating that it would be a "Woodstock West".

The Woodstock festival had taken place in Bethel, New York, in mid-August, almost four months earlier.

The event is remembered for its use of Hells Angels as security and its significant violence, including the stabbing death of Meredith Hunter and three accidental deaths: two from a hit-and-run car accident, and one from an LSD-induced drowning in an irrigation canal.

Scores were injured, numerous cars were stolen (and subsequently abandoned), and there was extensive property damage.

The concert featured performances (in order of appearance) by Santana, Jefferson Airplane, the Flying Burrito Brothers, and Crosby, Stills, Nash & Young (CSNY), with the Rolling Stones taking the stage as the final act.

The Grateful Dead were also scheduled to perform after CSNY, but shortly before their scheduled appearance, they chose not to due to the increasing violence at the venue. "That's the way things went at Altamont—so badly that the Grateful Dead, the prime organizers and movers of the festival, didn't even get to play," wrote staff at Rolling Stone magazine in a detailed narrative on the event, terming it, in an additional follow-up piece, "rock and roll's all-time worst day, December 6th, a day when everything went perfectly wrong."

Filmmakers Albert and David Maysles shot footage of the event and incorporated it into the 1970 documentary film titled Gimme Shelter.