"For What It's Worth (Stop, Hey What's That Sound)" (often referred to as simply "For What It's Worth") is a song written by Stephen Stills. It was performed by Buffalo Springfield, recorded on December 5, 1966, and released as a single on Atco Records in January 1967. The single peaked at number seven on the Billboard Hot 100 chart. This song is currently ranked number 63 on Rolling Stone's list of The 500 Greatest Songs of All Time as well as the eighth best song of 1967 by Acclaimed Music.

It was later added to the March 1967 second pressing of their first album, Buffalo Springfield. The title does not appear in the lyrics as it was added after the song was written.

Although "For What It's Worth" is often used as an anti-war song, Stephen Stills was inspired to write the track because of the Sunset Strip curfew riots in November 1966, a series of early counterculture-era clashes that took place between police and young people on the Sunset Strip in Hollywood, California, beginning in the mid-1966, the same year Buffalo Springfield had become the house band at the Whisky a Go Go on the Sunset Strip. It was within this period that local residents and businesses had become increasingly annoyed by late-night traffic congestion caused by crowds of young people going to clubs and music venues along the Strip. In response, they lobbied the city to pass local ordinances that stopped loitering and enforced a strict curfew on the Strip after 10pm. Young music fans, however, felt that the new laws were an infringement of their civil rights.

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