Don't Break the Oath is Mercyful Fate's second full-length album. It was released in 1984.
The style Mercyful Fate employed on Don't Break the Oath resembled a mixture of heavy metal with progressive elements, lyrically preoccupied with Satan and the occult and distinguished by King Diamond's theatrical falsetto vocals. The album was remastered and subsequently re-issued on Roadrunner Records in 1997. This reissue came with the bonus track "Death Kiss (Demo)", which would eventually evolve into the album's lead-off track, "A Dangerous Meeting". Metal-Rules.com named this the greatest extreme metal album of all time.