The Human Be-In is held in San Francisco's Golden Gate Park on January 14, 1967, launching the "Summer of Love." The event draws more than 20,000 people to enjoy peace, love, music and psychedelics.

Artist Michael Bowen advertised his event in the underground newspaper the San Francisco Oracle as "A Gathering of Tribes for the Human Be-In." He hoped to bring together the "tribes" of the psychedelic San Francisco hippies and the Berkeley anti-war activists. The immediate provocation for the Be-In was the banning of LSD by the California State Legislature in 1966. The Human Be-In embodied elements of 1960s counterculture, from psychedelic drug use, peace, love, and rock & roll, to civil rights sit-ins and teach-ins, antiwar protests and experimental performance art.

Between 20,000 and 30,000 people gathered on the polo fields of San Francisco's Golden Gate Park for the day-long event. The only infrastructure was a flatbed truck and an amp, which served as a stage for the musical acts and speakers. Countercultural icons such as Timothy Leary, Ram Dass and Allen Ginsberg addressed the crowd. Timothy Leary, the psychologist and advocate for LSD, shared his famous phrase "turn on, tune in, drop out" for the first time in public. Bands including the Grateful Dead, Jefferson Airplane and Big Brother and the Holding Company performed sets for their fans, many of whom were smoking weed or dropping acid.

The organizers lied to the city in order to get a permit for the event, and claimed it was for a local attorney's birthday party; therefore there was no police presence. Hell's Angels, however, were there to provide security.

The Human Be-In opened the door for much of what followed during the "Summer of Love" of 1967. Young people flocked to San Francisco, with flowers in their hair, to join the famous ranks of the hippies in Haight-Ashbury. The success of the Be-In led to many riffs on the theme, including numerous "Love-Ins," John Lennon and Yoko Ono's "Bed-In," and the TV show "Laugh-In." San Francisco was recognized as the capital of American counterculture, not only for drug use and flower power, but also for its boisterous and innovative music venues and protests against the Vietnam War.

The Human Be-In also led directly to the first rock festivals in the US, both held during the Summer of Love of 1967 in the Bay Area. The first was the Fantasy Fair and Magic Mountain Music Festival in Mount Tamalpais on June 10-11, 1967, featuring Jefferson Airplane, the Doors, and the Byrds.  The next, much larger, festival was Monterey Pop, which featured a who's who of rock artists, including Janis Joplin and Jimi Hendrix with a flaming guitar. By the time of Woodstock in 1969, when the counterculture rock festival reached the east coast, the glow of San Francisco's "Summer of Love" was already fading. Already in October 1967, San Francisco hippies staged a fake funeral, "The Death of the Hippie," in reaction to media coverage. That same month, Michael Bowen, the organizer of the Human Be-In, distributed 200 pounds of daisies to Vietnam War protesters at the Pentagon, resulting in some of the most iconic photos of the era.