Roger McGuinn of the Byrds, among the most important figures associated with Folk Rock, has often described how in conceiving his group’s sound he married his interest in Folk music with an emergent love for the Beatles. The result can be heard in the Byrds' debut of 1965. The first single from that recording, “Mr. Tambourine Man,” is a song written by Bob Dylan that features the kind of rich harmonies heard on the Beatles’ hits. If it was a formula of a kind, it was a formula that took the Byrds to the top of the charts. It spoke not just to the wide musical interests of the moment but to the latest phase in an emerging youth culture.
Before the Byrds — and other acts associated with Folk Rock such as the Mamas and the Papas, Simon and Garfunkel, and the Turtles — there was a popular Folk movement in the mid-50s that centered around performers like the Weavers, the Kingston Trio, and Harry Belafonte. On college campuses and in coffee houses, Folk music became a kind of alternative culture. Folk had its variants, to be sure. In the hands of Pete Seeger, a member of the Weavers, Folk music was more explicitly politicized than in the hands of, say, the Kingston Trio. Seeger was "blacklisted" for his efforts.
Generally speaking, however, the modern interest in Folk culture as a thing of "authenticity," removed from the commercial mainstream, is a recurring theme from the late 19th century forward. Folk Rock could be viewed as one moment in a longer history. But it's a moment that sees elements of Folk come up against and into the very cultural mainstream against which it was originally a reaction. As such, it was the kind of interaction that set Rock and Roll apart from much of popular culture's other offerings.