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.

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.