"How Long" is a song by American singer-songwriter JD Souther. Written in 1971, it was originally recorded by Souther for his 1972 debut solo album, John David Souther. It was given a limited release as a promotional 7-inch 45 rpm single in 1972 with Souther's "The Fast One" on the B-side.
The Eagles, longtime friends and collaborators with Souther, frequently performed "How Long" in concert during the early and mid-1970s. In 2007, the band covered the song for their album Long Road Out of Eden, the group's first full studio album since 1979. A year later, their version of the song won the Grammy Award for Best Country Performance by a Duo or Group with Vocal. It was the band's first Grammy since 1979.