The Incredible String Band was formed in 1965 by Scottish folk musicians Robin Williamson, Mike Heron and Clive Palmer. They recorded their eponymous debut album in 1966, a lighthearted affair which revealed only the merest hint of the psychedelic adventures to come. After that, the band broke up. Palmer decamped for the Trail to Afghanistan and Williamson visited Morocco from where he returned laden with exotic instruments like the famous gimbri, which was, much later, eaten by rats. In 1967 Heron and Williamson recorded The 5000 Spirits or the Layers of the Onion, an audaciously eclectic mix of bookish folk music, hippy love songs and Eastern modalities. They soon became the-name-to-drop-in-interviews for luminaries such as Paul McCartney and Bob Dylan. In their annum mirabilis of 1968 they practically defined the hippy counterculture in the extraordinary albums The Hangman's Beautiful Daughter and Wee Tam and the Big Huge. By then the group consisted of Williamson, Heron, Rose Simpson and Licorice McKechnie. They played at Woodstock in 1969 at the wrong time, having refused to play in the pouring rain the previous day (seen by manager Joe Boyd as a great missed opportunity). In 1970 Robin Williamson attempted to fuse the music with his theatrical fantasies in a quixotic multi-media spectacular at London's Roundhouse called U. It was "a surreal parable in dance and song" and highlighted the fact that they were never destined to make much money out of things. After that they lasted another 4 years. By 1974 tension between Williamson and Heron, who was pushing the band into prog-rock territory, had become unbearable and they split up.

Williamson soon formed "Robin Williamson and His Merry Band" which toured and released three albums of eclectic music with a Celtic emphasis. Within a few years, he went on to a solo career, moving increasingly into traditional Celtic styles. He also produced several recordings of humorous stories. Heron formed the rock group "Heron" and later released occasional solo albums. In 1997, the pair got back together for two concerts. This was followed by a full reunion of the original three members plus Williamson's wife Bina and Lawson Dando in 1999. By 2001 both Robin and Bina Williamson had left. Currently Heron, Palmer and Lawson, and new member Fluff tour regularly around the United Kingdom and internationally.

Those who believe in a cultural crossover between a particular axis of British hippie culture and an older, more spiritual idea of Britain have increasingly come to see the ISB as the focus of this unexpected crossover. This began in 1994 when Rose Simpson, a former member of the band, became Lady Mayoress of Aberystwyth, and reached a new level in the autumn of 2003 when the Archbishop of Canterbury, Dr Rowan Williams, wrote a foreword for a full length book about the band, Be Glad: An Incredible String Band Compendium (Helter Skelter Books), describing them as "holy" (he had previously chosen the ISB track "The Hedgehog's Song" as one of his pieces of music when he appeared on Desert Island Discs, broadcast Sunday 22 December 2002). Some have seen this as proof of the late Ian MacDonald's claim that "much that appeared to be profane in Sixties youth culture was quite the opposite".