Led Zeppelin: John Paul Jones (bass instrument); Jimmy Page, John Bonham, Robert Plant.

Personnel: Robert Plant (vocals, harmonica); Sandy Denny (vocals); Jimmy Page (guitar, acoustic guitar, electric guitar); John Paul Jones (keyboards, synthesizer); John Bonham (drums).

Additional personnel: Ian Stewart (piano); Sandy Denny (background vocals).

Audio Mixers: George Chkiantz; Andy Johns.

Audio Remasterer: Jimmy Page.

Liner Note Author: Masa Ito.

Recording information: Headley Grange, Hampshire, England (1971); Island Studios, London, England (1971); Rolling Stones Mobile Studio (1971); Sunset Sound, Hollywood, CA (1971).

Illustrator: Barrington Coleby.

Encompassing heavy metal, folk, pure rock & roll, and blues, Led Zeppelin's untitled fourth album is a monolithic record, defining not only Led Zeppelin but the sound and style of '70s hard rock. Expanding on the breakthroughs of III, Zeppelin fuse their majestic hard rock with a mystical, rural English folk that gives the record an epic scope. Even at its most basic -- the muscular, traditionalist "Rock and Roll" -- the album has a grand sense of drama, which is only deepened by Robert Plant's burgeoning obsession with mythology, religion, and the occult. Plant's mysticism comes to a head on the eerie folk ballad "The Battle of Evermore," a mandolin-driven song with haunting vocals from Sandy Denny, and on the epic "Stairway to Heaven." Of all of Zeppelin's songs, "Stairway to Heaven" is the most famous, and not unjustly. Building from a simple fingerpicked acoustic guitar to a storming torrent of guitar riffs and solos, it encapsulates the entire album in one song. Which, of course, isn't discounting the rest of the album. "Going to California" is the group's best folk song, and the rockers are endlessly inventive, whether it's the complex, multi-layered "Black Dog," the pounding hippie satire "Misty Mountain Hop," or the funky riffs of "Four Sticks." But the closer, "When the Levee Breaks," is the one song truly equal to "Stairway," helping give IV the feeling of an epic. An apocalyptic slice of urban blues, "When the Levee Breaks" is as forceful and frightening as Zeppelin ever got, and its seismic rhythms and layered dynamics illustrate why none of their imitators could ever equal them. ~ Stephen Thomas Erlewine

Led Zeppelin's epochal fourth album finds both the band's blues-rock thunder and their gentler, more lyrical side filed down to a razor-sharp point. "Black Dog" and "Rock and Roll" aren't just perennial air-guitar anthems; they're the ultimate distillation of the blues-inflected, hard-rock fury the band had already been perfecting for the past three years. Robert Plant's Little Richard-on-amphetamines wail rides perfectly atop the band's strategically directed crunch for maximum impact. "When the Levee Breaks"is a titanic take on the blues, with John Bonham's thunderous drums echoing through the subsequent decades. The folkier, acoustic tracks provide welcome moments of beauty and respite, and all the elements of the band's sound come together in "Stairway to Heaven," a suite of shifting dynamics that would become the Eiffel Tower of classic-rock radio forevermore.