Formed by the addition of Neil Young to the existing Crosby, Stills and Nash folk-rock supergroup in 1969.

CSN had achieved significant success with their first album, Crosby, Stills & Nash in early 1969. However, apart from drummer Dallas Taylor, Stills had contributed most of the instrumental parts on the album, which left the band needing additional personnel in order to be able to tour. Retaining Taylor, the band decided initially to hire a keyboard player, Stills at one point approaching Steve Winwood, who declined.

Over dinner with Ahmet Ertegün, the Atlantic label head suggested Canadian singer/songwriter Neil Young, who was also managed by CSN's manager Elliot Roberts, as a fairly obvious choice. Initial reservations were held by Stills and Nash, Stills owing to his history with Young in Buffalo Springfield, Nash due to his not knowing Young at all outside of his work. But after several meetings, the trio expanded to a quartet with Young a full partner, but with the terms allowing Young full freedom to maintain a parallel career with his new back-up band, Crazy Horse.

The quartet went on tour in the late summer of 1969, their second gig being the Woodstock Festival, which was highly acclaimed. By contrast, little mention is made of the group's subsequent appearance at Altamont, CSNY having escaped mostly unscathed from the fallout of that debacle.

Great anticipation had built for the group, and their first album with Young, Déjà Vu, was released in March 1970 to great acclaim, topping the charts and generating three hit singles.

The group also became politically active, with protest against both the establishment and the Vietnam War gearing up. While staying at a house down the peninsula from San Francisco, the reports of the Kent State shootings reached Young and Crosby, inspiring Young to write his protest classic Ohio, recorded and released weeks later and another Top 20 hit for the group.

The group found themselves in the position of enjoying a level of adulation far greater than experienced with their previous bands. The collective talents allowed the band to straddle all the flavours of popular music of the period, from country-rock to ballads and both acoustic and electric. Indeed, with the Beatles break-up and with Bob Dylan in reclusive low-key activity since mid-1966, CSNY found itself as the adopted standard bearers for their generation. An entire sub-industry of singer-songwriters in California either had their careers boosted or came to prominence in the wake of CSNY, among them Joni Mitchell, Jackson Browne and the Eagles. All were managed by Roberts and signed to Geffen’s Asylum label.

However, the tenuous nature of the partnership, built into the group philosophy from the onset and strained by their success, weighed on the individual personalities and the group imploded after their tour in the summer of 1970. Concert recordings from that tour ended up on the 1971 double album 4 Way Street, but the group never completely recaptured momentum as years would pass between trio and quartet recordings.

In the early 1970s, all four members released well-received solo albums. Crosby and Nash embarked on a successful acoustic tour accompanied only by their own guitars and piano, captured for the 1998 document Another Stoney Evening. On tour, they rediscovered the joy they had felt with CSN at first, minus the egotistic in-fighting that had made the last CSNY shows so difficult.

In June/July 1973, the four reunited in Hawaii for a working vacation, ostensibly to record a new CSNY album, tentatively titled Human Highway. Recording at Young’s ranch, the bickering that had sunk the band in 1970 resumed, scattering the group and leaving Young to recall Crazy Horse for his Tonight's The Night tour.

Roberts finally persuaded the quartet to reassemble once again in the summer of 1974, with sidemen Tim Drummond on bass, Russ Kunkel on drums and Joe Lala on percussion, to embark on the first-ever outdoor stadium tour, arranged by San Francisco impresario Bill Graham.

However, all was not well. An attempt at a new CSNY album in the fall was scrapped, the label having compiled So Far to have something to promote during the tour.

Reaching an impasse with the parent band, Crosby and Nash decided to re-activate their duo act, touring regularly, signing to ABC Records and producing two additional studio albums. Stills and Young returned to their own careers, with Young in particular achieving great success in adapting to changing musical tastes. They also united for a one-off tour and album credited to The Stills-Young Band, Long May You Run. Initially, the album started life in the spring of 1976 in Miami as the third attempt at a CSNY reunion, but when Crosby and Nash had to return to LA to finish Whistling Down the Wire, Stills and Young wiped the vocal contributions by the other pair off the master tape.

The old tensions between Stills and Young, dating back the the Buffalo Springfield days, resurfaced, exacerbated by Stills’ choice of professional studio musicians to back them rather than Young’s preferred Crazy Horse. After a show in July 1976, Young abandoned the tour.

CSN resurfaced without Young in 1977 to release the album CSN. Regrouping as a regular touring act, they charted again with Daylight Again in 1982. However, Crosby's increasing dependence on cocaine was making his participation problematic and he was jailed on drug and weapons charges in Texas in May 1982.

On a promise to Crosby, Young agreed to rejoin the trio in the studio upon Crosby’s release from prison for American Dream in 1988. However, Stills and Crosby were barely functioning and the album received poor critical notices, and Young refused to support it with a CSNY tour.

CSN recorded two more studio albums in the 1990s, Live It Up and After The Storm, both low sellers by previous standard and mostly ignored by all except for their remaining core fans. A well-conceived box set arrived in 1991, but manager Roberts, no longer with the trio but still representing Young, pulled most of Young’s material earmarked for the box and only seven CSNY songs in total remained to be included.

By the late 1990s, CSN found themselves without a record contract. They began financing recordings themselves, and in 1999 Stills invited Young to guest on a few tracks. Young increased his level of input, turning the album into a CSNY project, Looking Forward, released on Young's label Reprise Records. With writing credits mostly limited to band members, the disc was better received than the previous three albums, and the ensuing CSNY2K tour in 2000 and the CSNY Tour of America of 2002 were major successes.

In 2006, CSNY set off on their Freedom of Speech tour in support of Young's album Living with War. The long setlists included the bulk of the new protest album as well as material from Stills' long delayed solo album Man Alive! and newer material from Crosby and Nash.