Twenty years ago, Bono described Achtung Baby as 'the sound of four men chopping down The Joshua Tree' while Jon Pareles of the New York Times wrote that 'stripped-down and defying its old formulas, U2 has given itself a fighting chance for the 1990's'.

The album won a Grammy Award for Best Rock Performance and became one of the most significant records of the nineties and of U2’s career.

To mark twenty years since its 1991 release, an anniversary edition of U2’sAchtung Baby is due on October 31, 2011.

Recorded over six months at Hansa Studio in Berlin and Windmill Lane in Dublin, Achtung Baby is U2’s seventh studio album. Produced by long time U2 collaborators, Daniel Lanois and Brian Eno with Steve Lillywhite, Achtung Babywas engineered by Flood and led by The Fly.

The album spawned four other singles, Mysterious Ways, One, Even Better Than The Real Thing and Who’s Gonna Ride Your Wild Horses.

The Achtung Baby archives have unearthed some previously unreleased songs from the recording sessions.

With a raft of unreleased material; video, remixes, b-sides and documentary footage discovered, a full album of demo and early versions of the final 1991 tracklisting has also been revealed. Five physical editions including vinyl, CD, DVD and digital options will be made available.

Earlier this year U2 returned to Hansa Studio in Berlin to discuss Achtung Babyin From The Sky Down, directed by Academy Award winning director Davis Guggenheim (Waiting for Superman, An Inconvenient Truth). The film has been selected to open the Toronto International Film Festival on September 8th and will be included in the anniversary edition.