Stephen Arthur Stills (born January 3, 1945) is an American musician and multi-instrumentalist best known for his work with Buffalo Springfield and Crosby, Stills, Nash & Young.

Beginning his professional career with Buffalo Springfield, he composed their only hit "For What It's Worth," which became one of the most recognizable songs of the decade. Other notable songs he contributed to the band were "Sit Down, I Think I Love You," "Bluebird" and "Rock & Roll Woman." According to Richie Furay, he was "the heart and soul of Buffalo Springfield."

After Buffalo Springfield broke up, Stills began working with David Crosby and Graham Nash on their debut album. Stills, in addition to writing much of the album, played bass, guitar, and keyboards on most of the album. The album sold over four million copies and at that point, had outsold anything from the three members' prior bands: The Byrds, Buffalo Springfield, and The Hollies. The album won the trio a Grammy Award for Best New Artist.

Neil Young, formerly of Buffalo Springfield, joined CSN months later for their second concert at Woodstock and subsequent album Déjà Vu. The album found Stills again as a leader of the group. Living up to his nickname "Captain Many Hands" he played bass, guitar and keyboard on the title track, and electric guitar and piano on Helpless. Young appeared on half of the album, which became a huge success and sold over eight million copies. In its wake all four members of CSNY released solo albums that reached the top 20, while Young in particular found major success as a solo artist from this point forward.

Stills' first solo album Stephen Stills went gold and is the only album to feature both Jimi Hendrix and Eric Clapton. Its hit single, "Love The One You're With" became his biggest solo hit peaking at No. 14 in the Billboard Hot 100. A string of solo albums, and a band with Chris Hillman called Manassas followed in 1972. In the summer of 1974 Young reunited with CSN after a four-year hiatus for a concert tour which was recorded and released in 2014 as CSNY 1974. It was one of the first ever stadium tours, and the largest tour the band has done to date. CSN reunited in 1977 for their album CSN which became the trio's best selling record. CSN(Y) continued to have platinum albums through the 1980s. Stills' solo career and bands have combined sales of over 35 million albums to date.

Stills was ranked #28 in Rolling Stone Magazine's 2003 list of "The 100 Greatest Guitarists of All Time" and #47 in the 2011 list. Stills became the first person to be inducted twice on the same night into the Rock and Roll Hall of Fame for his work with CSN and Buffalo Springfield. According to Neil Young, "Stephen is a genius."