Hysteria is the fourth studio album by English rock band Def Leppard, released on 3 August 1987 through Mercury Records. It is Def Leppard's best-selling album to date, selling over 20 million copies worldwide, including 12 million in the US, and spawning seven hit singles. The album charted at number one on both the Billboard 200 and the UK Albums Chart.

Hysteria was produced by Robert John "Mutt" Lange. The title of the album was thought up by drummer Rick Allen, referring to his 1984 car accident, the amputation of his arm, and the ensuing worldwide media coverage surrounding it. It is the last album to feature guitarist Steve Clark before his death, although songs co-written by him would appear on the band's next album, Adrenalize.

The album is the follow-up to the band's 1983 breakthrough Pyromania. Hysteria's creation took over three years and was plagued by delays, including the aftermath of drummer Rick Allen's accident that cost him his left arm on 31 December 1984. Subsequent to the album's release, Def Leppard published a book titled Animal Instinct: The Def Leppard Story, written by Rolling Stone magazine senior editor David Fricke, on the three-year recording process of Hysteria and the tough times the band endured through the mid-1980s. Lasting 62 minutes and 32 seconds, the album is the band's longest to date.