Psychedelic rock is a style of rock music that is inspired or influenced by psychedelic culture and attempts to replicate and enhance the mind-altering experiences of psychedelic drugs. It emerged during the mid 1960s among folk rock and blues-rock bands in United States and the United Kingdom. It often used new recording techniques and effects and drew on non-Western sources such the ragas and drones of Indian music. Psychedelic rock bridged the transition from early blues- and folk music-based rock to progressive rock, glam rock, hard rock and as a result influenced the development of sub-genres such as heavy metal. Since the late 1970s it has been revived in various forms of neo-psychedelia.

In the 1960s, in the tradition of jazz and blues, many folk and rock musicians began to take drugs and included drug references in their songs. Beat Generation writers like William Burroughs, Jack Kerouac, Allen Ginsberg and especially the new proponents of consciousness expansion such as Timothy Leary, Alan Watts and Aldous Huxley, profoundly influenced the thinking of the new generation, helping to popularise the use of LSD. Psychedelic music's LSD-inspired vibe began in the folk scene, with the New York-based Holy Modal Rounders using the term in their 1964 recording of "Hesitation Blues". The first group to advertise themselves as psychedelic rock were the 13th Floor Elevators from Texas, at the end of 1965. The term was first used in print in the Austin American Statesman in an article about the band titled "Unique Elevators shine with psychedelic rock", dated 10 February 1966, and theirs was the first album to use the term as part of its title, in The Psychedelic Sounds of the 13th Floor Elevators, released in August that year. Members of the Beatles began experimenting with LSD from 1965 and the group introduced many of the major elements of the psychedelic sound to audiences in this period, with "I Feel Fine" (1964) using guitar feedback; "Norwegian Wood" from their 1965 Rubber Soul album using a sitar, and the employment of backwards spooling on their 1966 single B-side "Rain". Drug references began to appear in their songs from "Day Tripper" (1965) and more explicitly from "Tomorrow Never Knows" (1966) from their 1966 album Revolver.

The Byrds, emerging from the Californian folk scene, and the Yardbirds from the British blues scene, have been seen as particularly influential on the development of the genre. The psychedelic life style had already developed in California, particularly in San Francisco, by the mid-60s, where there was also an emerging music scene. This moved out of acoustic folk-based music towards rock soon after The Byrds "plugged in" to produce a chart topping version of Bob Dylan's "Tambourine Man" in 1965. As a number of Californian-based folk acts followed them into folk-rock they brought their psychedelic influences with them to produce the "San Francisco Sound". Particularly prominent products of the scene were The Grateful Dead, Country Joe and the Fish, The Great Society, Big Brother and the Holding Company, The Charlatans, Moby Grape, Quicksilver Messenger Service and Jefferson Airplane. The Byrds rapidly progressed from purely folk rock in 1966 with their single "Eight Miles High", which made use of free jazz and Indian ragas and the lyrics of which were widely taken to refer to drug use.[9] In Britain The Yardbirds, with Jeff Beck as their guitarist, increasingly moved into psychedelic territory, adding up-tempo improvised "rave ups", Gregorian chant and world music influences to songs including "Still I'm Sad" (1965) and "Over Under Sideways Down" (1966) and singles: "Shapes of Things" (1966) and "Happenings Ten Years Time Ago" (1966).[17] They were soon followed into this territory by bands such as Procol Harum, The Moody Blues and The Nice.