Turn On, Tune In, Drift Off: Ambient Music's Psychedelic Past rethinks the history and socioaesthetics of ambient music as a popular genre with roots in the psychedelic countercultures of the late twentieth century. Victor Szabo reveals how anglophone audio producers and DJs between the mid-1960s and century's end commodified drone- and loop-based records as "ambient audio": slow, spare, spacious audio sold as artful personal media for creating atmosphere, fostering contemplation, transforming awareness, and stilling the body. The book takes a trip through landmark ambient audio productions and related discourses, including marketing rhetoric, artist manifestos and interviews, and music criticism, that during this time plotted the conventions of what became known as ambient music. These productions include nature sounds records, experimental avant-garde pieces, "space music" radio, psychedelic and cosmic rock albums, electronic dance music compilations, and of course, explicitly "ambient" music, all of which popularized ambient audio through vivid atmospheric concepts. In paying special attention to the sound of ambient audio; to ambient audio's relationship with the psychedelic, New Age, and rave countercultures of the US and UK; and to the coincident evolution of therapeutic audio and "head music" across alternative media and independent music markets, this history resituates ambient music as a hip highbrow framing and stylization of ongoing practices in crafting audio to alter consciousness, comportment, and mood. In so doing, Turn On, Tune In, Drift Off illuminates the social and aesthetic rifts and alliances informing one of today's most popular musical experimentalisms.