Rick Savage, Tony Kenning, and Pete Willis, all students at Tapton School in Sheffield, South Yorkshire, formed a band called Atomic Mass in 1977. The band originally consisted of Willis on guitar, Savage on bass (after originally playing guitar), and Kenning on drums. Only 18 at the time, Joe Elliott tried out for the band as a guitarist following a chance meeting with Willis after missing a bus. During his audition it was decided that he was better suited to be the lead singer. Their first ever gig was in the dining hall in A Block in Westfield School in Mosborough, Sheffield.

Soon afterward they adopted a name proposed by Elliott, "Deaf Leopard", which was originally a band name he thought up while writing reviews for imaginary rock bands in his English class (and in at least partial reference to the band Led Zeppelin). At Kenning's suggestion, the spelling was slightly modified in order to make the name seem less like that of a punk band. In January 1978, Steve Clark joined the band. According to Joe Elliott, he successfully auditioned for the band by playing Lynyrd Skynyrd's "Free Bird" in its entirety.

In November, just prior to recording sessions for what would be a three-song release known as The Def Leppard E.P., Kenning abruptly left the band; he would later form the band Cairo. He was replaced for those sessions by Frank Noon. By the end of the month, Rick Allen, then only 15 years old, had joined the band as its full-time drummer. Sales of the EP soared after the track "Getcha Rocks Off" was given extensive airtime by renowned BBC Radio DJ John Peel, considered at the time to be a champion of punk rock and new wave music.

Throughout 1979, the band developed a loyal following among British hard rock and heavy metal fans and were considered among the leaders of the New Wave of British Heavy Metal movement. Their growing popularity led to a record deal with the major label Phonogram/Vertigo (Mercury Records in the US). Leppard's original management, MSB, a local duo consisting of Pete Martin and Frank Stuart-Brown, were fired after Martin and Joe Elliott got into a fist fight over an incident on the road. The band approached Peter Mensch of Leber-Krebs management, who had booked them on a tour of the UK supporting AC/DC. Mensch, who admitted that he had had his eye on the band, became their manager.

Def Leppard's debut album, On Through the Night, was released on 14 March 1980. Although the album hit the Top 15 in the UK, many early fans were turned off by the perception that the band was trying too hard to appeal to American audiences by recording songs like "Hello America" and touring more in the US (supporting Pat Travers, AC/DC, and Ted Nugent). A performance at the Reading Festival in August was marred when audience members expressed their displeasure by pelting the band with beer cans and bottles filled with urine. This incident was partially blamed on a cover story in Sounds music newspaper by the journalist Geoff Barton entitled "Has the Leppard changed its spots?" accusing the band of selling out to the American market. In a documentary on the band recorded for BBC 2, Barton recalls feelings of guilt over the story and having a "stand-up row" with the band's manager, Mensch, backstage at the show. In the documentary series Metal Evolution, Joe Elliot says that the media had exaggerated the event and all bands on the day had experienced the 'abuse' from the crowd.

The band had by then caught the attention of AC/DC producer Robert John "Mutt" Lange, who agreed to work on their second album, High 'n' Dry, released on 11 July 1981. Lange's meticulous approach in the studio helped them begin to define their sound. Despite the album's unimpressive sales figures, the band's video for "Bringin' On the Heartbreak" became one of the first metal videos played on MTV in 1982, bringing the band increased visibility in the U.S. After the album's release, a European tour followed. The band opened for Ozzy Osbourne and Blackfoot.

Phil Collen, former guitarist with the glam band Girl, on 12 July 1982 replaced Pete Willis, who had been fired the previous day because of excessive alcohol consumption on the job. (Willis would later resurface with the bands Gogmagog and Roadhouse.) This personnel change took place during the recording of their third album, Pyromania, which was released on 20 January 1983 and also produced by Lange. The cover artwork depicted an animated picture of a huge flame emerging from the top floor of a skyscraper, with a bullseye aimed at the flame. Though many stores would not carry the album due to the cover, the band did not change the artwork. The lead single, "Photograph", turned Def Leppard into a household name, supplanting Michael Jackson's "Beat It" as the most requested video clip on MTV and becoming a staple of rock radio (dominating the US Album Rock Charts for six weeks), and sparked a headline tour across the U.S.

Fueled by "Photograph" and subsequent singles "Rock of Ages" and "Foolin'", Pyromania went on to sell six million copies in 1983 (more than 100,000 copies every week in that year) and was held off the top of the US album charts only by Michael Jackson's Thriller. With the album's massive success, Pyromania was the catalyst for the 1980s pop-metal movement. In 2004, Pyromania was certified Diamond having sold over 10 million copies in the US. Def Leppard's US tour in support of Pyromania began opening for Billy Squier in March and ended with a headlining performance before an audience of 55,000 at Jack Murphy Stadium in San Diego, California in September. As a testament to the band's popularity at the time, a US Gallup poll in 1984 saw Def Leppard voted as favourite rock band over peers such as The Rolling Stones, AC/DC, and Journey. However, in their native England, Duran Duran secured the number one spot.

Following their breakthrough, the band moved to Dublin in February 1984 for tax purposes to begin writing the follow-up to Pyromania. Mutt Lange initially joined in on the songwriting sessions but then suddenly declined to return as producer due to exhaustion. Instead, Jim Steinman (of Meat Loaf's Bat out of Hell fame) was brought in.

On 31 December 1984, drummer Rick Allen lost his left arm in a car crash on the A57 in the hills outside the band's home city Sheffield, when his Corvette swerved off the road on a sharp bend and went through a drystone wall. Despite the severity of the accident, Allen was committed to continuing his role as Def Leppard's drummer, and realised that he could use his legs to do some of the drumming work previously done with his arms. He then worked with Simmons to design a custom electronic drum kit. The other members of the band supported Allen's recovery and never sought a replacement. Allen was placed in a separate studio to practice his new drums. After a few months, Allen gathered the band together and performed the intro to the Led Zeppelin version of "When the Levee Breaks" to showcase his progress to the band. Joe Elliott reports this as being a "very emotional moment." During this period, Mutt Lange returned as producer. Def Leppard brought in Jeff Rich in August 1986 to play alongside Allen during Def Leppard's warm-up mini tour of Ireland, but after Rich accidentally missed a gig, he and the band realised Allen could drum alone. Allen's comeback was sealed at the 1986 Monsters of Rock festival in England, with an emotionally charged ovation after his introduction by Joe Elliott.

After over three years of recording, Def Leppard's fourth album, Hysteria, was released on 3 August 1987. In the UK, the first single from the album, "Animal", became the band's first Top 10 hit in their native UK, reaching No. 6 on the UK Singles Chart. "Animal" also started their run of ten consecutive U.S. Billboard Hot 100 Top 40 singles. Hysteria immediately topped the UK Album Charts in its first week of release. However, US album sales were relatively slow (compared to Pyromania) until the release of the fourth single, "Pour Some Sugar on Me". The song hit Number 2, and Hysteria finally reached the top of the U.S. Billboard 200 in July 1988. The "Pour Some Sugar on Me" video was No. 1 on Dial MTV for a record 73 days (from 26 May–5 September 1988). Often regarded as the band's signature song, "Pour Some Sugar on Me" was ranked No. 2 on VH1's "100 Greatest Songs of the 80s" in 2006. In October 1988, the power ballad "Love Bites" became Def Leppard's first (and only) number one single on the Billboard Hot 100, and in January 1989, the band scored another US Top 5 hit with "Armageddon It". Wanting to give fans something new after the massive radio and video airplay for not only the 6 singles but also the Album tracks that Radio DJs were playing off the album, the band performed "Tear It Down", a Hysteria B-side at the 1989 MTV Video Music Awards. Due to positive fan reaction the song was reworked for their following album Adrenalize.

Hysteria is one of only a handful of albums that has charted seven singles or more on the US Hot 100: "Women" (#80), "Animal" (#19), "Hysteria" (#10), "Pour Some Sugar on Me" (#2), "Love Bites" (#1), "Armageddon It" (#3), and "Rocket" (#12). It remained on the charts for three years and has sold over 20 million copies worldwide. Equally successful was the accompanying 15-month tour, in which the band performed in the round. This concept proved wildly popular with fans (as seen in the videos for "Pour Some Sugar on Me" and "Armageddon It") and was used again for the Adrenalize tour.

At the 1989 Brit Awards held at the Royal Albert Hall in London, Def Leppard were a nominee for Best British Group, and the band performed "Pour Some Sugar on Me" at the ceremony. At the 1989 American Music Awards, Def Leppard won Favorite Heavy Metal/Hard Rock Artist, as well as Favorite Heavy Metal/Hard Rock Album (for Hysteria).

Following Hysteria, the band quickly set out to work on their fifth album, hoping to avoid another lengthy gap. Steve Clark's alcoholism worsened to the point that he was constantly in and out of rehab. Recording sessions suffered from this distraction, and in mid-1990, Steve was granted a six-month leave of absence from the band. Clark died from an accidental mix of prescription drugs and alcohol on 8 January 1991, in his London home.

The remaining band members decided to carry on and recorded the album as a four-piece, with Collen mimicking Clark's style on his intended guitar parts. Def Leppard's fifth album, Adrenalize, was finally released on 31 March 1992. The album simultaneously entered at Number one on both the UK and US album charts, staying on the latter for 5 weeks. The first single, "Let's Get Rocked", was an instant smash hit, and the band performed the song at the 1992 MTV Video Music Awards where it was nominated for Best Video of the Year. In April 1992, Def Leppard appeared at the Freddie Mercury Tribute Concert at Wembley Stadium, London, performing a three-song set of "Animal", "Let's Get Rocked" and Queen's "Now I'm Here" with guitarist Brian May. Joe Elliott later performed "Tie Your Mother Down" with the remaining members of Queen and Guns N' Roses guitarist Slash.

In 1992 auditions to replace Clark commenced. Among the guitarists who auditioned included Adrian Smith, John Sykes, and Gary Hoey. Ultimately, the band chose Vivian Campbell, formerly of Dio and Whitesnake. Another world tour followed but the band's fortunes began to be affected by the rise of alternative rock, including grunge.

A collection of b-sides and unreleased tracks recorded between 1984 and 1993, called Retro Active, was released in October 1993, preceded by the success of "Two Steps Behind" (from the Arnold Schwarzenegger film Last Action Hero). Another single, "Miss You in a Heartbeat", hit the Top 5 in Canada, becoming one of their biggest hits there. Retro Active has sold 3 million copies worldwide to date. Two years later, Def Leppard issued their first greatest hits collection, Vault: Def Leppard Greatest Hits (1980–1995), which reached number 3 in the UK, and sold over 5 million copies in the US. Alternate track listings of the album were issued for North America, the UK, and Japan. The compilation included a new track, the power ballad "When Love & Hate Collide", which became their biggest ever hit in the UK, hitting No. 2 on the UK Singles Chart.

On 23 October 1995, the band entered the Guinness Book of World Records by performing three concerts on three continents in one day (Tangiers, Morocco; London, England; and Vancouver, Canada).

Slang, released in May 1996, marked a drastic musical departure for the band by featuring darker lyrics and a stripped-down alternative rock edge. The band rehearsed and played the songs together in the studio instead of recording parts separately, resulting in a much more live-sounding album. The US audience reception for Slang and its subsequent tour was a major dropoff from a decade earlier, but Q Magazine nonetheless listed Slang as one of their Top Ten Albums of 1996. This album was the first recorded performance of Rick Allen playing a semi-acoustic drum kit since his accident, and not his electronic set as was first used with Hysteria.

VH1 revived the band's fortunes in the US in 1998 by featuring them on one of the first episodes of Behind the Music. Reruns of the episode yielded some of the series' highest ratings and brought the band's music back into the public consciousness (following years of burial by the alternative rock climate). The episode was even parodied on Saturday Night Live. In an effort to capitalise on this new momentum, Def Leppard returned to its classic sound with the 1999 album Euphoria. The first single, "Promises", reunited the band with Mutt Lange and hit the US Mainstream Rock charts at No. 1 for 3 weeks. The album was certified gold in the US and Canada.

On 5 September 2000, Def Leppard were inducted into the Rock Walk of Fame on Hollywood's Sunset Boulevard by their friend Brian May of Queen. In 2001, VH1 produced and aired Hysteria - The Def Leppard Story, a biopic that included Anthony Michael Hall as Mutt Lange and Amber Valletta as Lorelei Shellist (Steve Clark's girlfriend). The docudrama covered the band's history between 1977 through 1986, recounting the trials and triumphs of Rick Allen and Steve Clark. The 18 July broadcast still produced some of the channel's highest-ever ratings and is available on DVD.

Def Leppard's tenth album, X, saw the band's musical direction moving more towards pop and further away from the band's hard rock roots. X quickly disappeared from the charts, ultimately becoming the band's least successful release. However, the accompanying tour played to the band's strongest audiences since Adrenalize.

An expanded and updated best-of collection, Best Of, was released internationally in October 2004. The North America-only version, Rock of Ages – The Definitive Collection, was released the following May. Def Leppard participated at the Live 8 show in Philadelphia and toured in the summer with Bryan Adams. In 2005, the band left their longtime management team, Q-Prime, and signed with HK Management.

On 23 May 2006, Def Leppard released an all-covers album titled Yeah!. The disc pays homage to classic rock songs of their childhood, originally recorded by Blondie, The Kinks, Sweet, ELO, and Badfinger among others. It debuted at No. 16 in the US, their tenth consecutive Top 20 album.

The band, along with Queen, Kiss, and Judas Priest, were the inaugural inductees of "VH1 Rock Honors" on 31 May 2006. During the show, The All-American Rejects paid homage to the band with a cover of "Photograph". Soon afterwards, they embarked on a US tour with Journey. That October, Hysteria was re-released in a two-disc deluxe edition format, which combined the original remastered album with b-sides, remixes, and bonus tracks from single releases. Def Leppard began their "Downstage Thrust Tour", on 27 June, which took them across the US and into Canada. Support bands were Foreigner and Styx.

Songs from the Sparkle Lounge was released worldwide on 28 April 2008 and on 30 April 2008 in Japan. The album debuted at No. 5 on The Billboard 200 in America. The first single was entitled "Nine Lives" and featured country singer Tim McGraw, who co-wrote the song with Joe Elliott, Phil Collen, and Rick Savage.

A tour in support of the album began on 27 March 2008 in Greensboro, North Carolina, with Styx and REO Speedwagon joining the band on US dates. The band also played several European rock festivals. An arena tour of the UK took place in June in which the band co-headlined with Whitesnake and was supported by US southern rockers Black Stone Cherry. The band then returned to Europe before coming back for a second leg of the UK tour in June. The first of these dates was at the Glasgow SECC on 17 June. Again they were joined by Whitesnake; however, hard rock band Thunder supported at some of these shows. Black Stone Cherry continued to support most of the dates, including some of the Thunder ones. Six shows which were cancelled during the USA/Canada leg of their world tour due to illnesses affecting Joe Elliott and Phil Collen would be rescheduled and played in August of that year. On 11 June, Def Leppard announced further dates for their 2008 World Tour. The extension saw them visit Japan, Australia and New Zealand. Whitesnake continued to support Def Leppard for their Indian and Japanese dates. Def Leppard toured 41 US cities plus Toronto, Canada, during mid-2009 with Poison and Cheap Trick and also played the Download Festival with Whitesnake and ZZ Top.

In October 2008, Def Leppard played with country star Taylor Swift in a taped show in Nashville, Tennessee, in a show called CMT Crossroads: Taylor Swift and Def Leppard. This was released as a DVD on 16 June 2009 exclusively at Wal-Mart. The release was the best-selling DVD of week, and the 10th best selling Wal-Mart music release. A fan of the band since childhood, Swift chose Def Leppard to perform together for the show, and their crossover performance of "Photograph" was up for both Performance of the Year and Wide Open Country Video of the Year at the CMT Music Awards in 2009. Swift said of the performance, "Performing with Def Leppard was awesome! They are the coolest guys on the planet! It was the coolest thing in the world to have my band on stage with them...It was the most amazing feeling in the world..." Joe Elliott from Def Leppard said, "What an absolute pleasure it was to work with Taylor and her band who are a great set of musicians. Myself and Taylor blended really well together, I think, and everybody, both bands and the crowd, had a great time. I'm really glad we had the opportunity to do this."

In October 2009 the band announced that they would be cancelling the last leg of the 2009 North American tour, a total of 23 shows. The band cited, "unforeseen personal matters," as the reason for the cancellations. The band has denied rumours about a breakup, saying, "We're not splitting. Not at all. We often joke, what else would we do? You just can't imagine doing anything else.".

On 22 February 2011 Mirrorball, a two-disc live album, with three new studio tracks, was released in parts of Europe on 3 June, the rest of Europe on 6 June, and on 7 June in the US; it was announced at the same time that Def Leppard would perform at the Download Festival on 10 June 2011. Three singles, all studio tracks, were released from the album, the first single being "Undefeated".

Def Leppard embarked on a two-month U.S. tour in the summer of 2011, with Heart., as well as another seven shows in Australia in October with The Choirboys and Heart, two shows in Japan in November, and six shows in the United Kingdom in December with Steel Panther and Mötley Crüe.

The following year, they then toured with Poison and Lita Ford in the US during the summer of 2012 from 20 June through 15 September, dubbed the "Rock Of Ages 2012 Tour". In between the tour, they headlined Rock Fest on 22 July with Poison and others.

The year after, Def Leppard played an eleven show residency at the Hard Rock Hotel and Casino in Las Vegas, Nevada from 22 March through 13 April 2013. The residency, referred to as Viva! Hysteria, featured a two part show, with the first half featuring Def Leppard opening for themselves, under the alias "Ded Flatbird", (jokingly called the best Def Leppard coverband in the world), when they would then play songs they very rarely play live, going all the way back to "Good Morning Freedom" from the Def Leppard E.P. in 1979, an era usually left untouched by the band. The opening set varied each night, from playing the best hits from albums like On Through the Night, Slang, and Euphoria, to being the entire first half of High 'n' Dry. The second half, and "main event" was Def Leppard, as themselves playing their best-selling album, Hysteria, from start to finish. A live album, also titled Viva! Hysteria was released on 22 October 2013. This was the first time the band has played an album live from start to finish.

The band has re-recorded several hits and even the entire album Hysteria in an effort to circumvent their record label from future royalties, though of these re-recordings, only Rock Of Ages, Pour Some Sugar On Me, and Hysteria (the song) have actually been released.

In June 2013, Vivian Campbell announced that he had developed Hodgkin's lymphoma, a malignant form of cancer that affects the Reed-Sternberg cells, located in the lymph nodes. He continued performing with Def Leppard, and no shows were canceled or rescheduled. The sole idea of cancelling any shows and not doing anything disgusted Vivian, believing performing would be the best way to remain optimistic. In November 2013, he announced he was in remission, however, the cancer has since reemerged, and he is now receiving chemotherapy once again. Should the cancer once again enter remission, he will undergo a stem-cell transplant.

On 11 February 2014, the band released a remastered deluxe edition of its 1996 album Slang after much delay. The album, still coveted by many loyal fans of the band, now features 30 tracks including demos, b-sides, and unreleased material.

From 23 June 2014 to 31 August 2014, Def Leppard and Kiss are scheduled to tour 42 cities, with a dollar per ticket donated to such military charities as Wounded Warrior Project.

At certain recent points in time, the band had projects, such a cartoon and a documentary, in development. However, these projects seemed to have been shelved. The band had originally planned to due another residency in Las Vegas, this time in honor of Pyromania (called Viva! Pyromania), but due to the "Heroes 2014" tour with Kiss, and an upcoming, unnamed studio album, the project has been pushed back indefinitely. The new album was originally planned to be an EP; it is to be completed by the end of 2014 and will be released the following year. The album's set-list has 15 songs as of June 2014, which will presumably be narrowed down.

Source : http://en.wikipedia.org/wiki/Def_Leppard