Def Leppard are an English hard rock band from Sheffield who formed in 1977 as part of the New Wave of British Heavy Metal. High sales of the albums Pyromania and Hysteria made Def Leppard one of the top selling rock bands of the 1980's.

The music of Def Leppard is a mixture of hard rock, glam rock, AOR, and heavy metal elements. The band has been associated with the pop metal movement of the 1980s and the contemporaneous NWOBHM genre of the late 1970s. The band's songs generally feature simple guitar hooks and catchy, melodic choruses. The Def Leppard sound is also characterised by its combination of hard rock and polished melodic backing vocals.

By the release of the Hysteria record, the band had developed a distinctive sound featuring heavily processed drums and effects-laden "space-age" guitar sounds, overlaid with a multi-layered wall of husky, harmonised vocals. Def Leppard is one of only five rock bands with two original albums selling over 10 million copies each in the U.S. The others are Led Zeppelin, Pink Floyd, Eagles and Van Halen.