"Enter Sandman" is a song by American heavy metal band Metallica. It was released as the first single from their fifth album, Metallica in 1991. The music was written by Kirk Hammett, James Hetfield and Lars Ulrich. Vocalist and rhythm guitarist Hetfield wrote the lyrics, which deal with the concept of a child's nightmares.

The single achieved platinum certification for more than 1,000,000 copies shipped in the United States, spurring sales of over 30 million copies for Metallica and propelling Metallica to worldwide popularity. Acclaimed by critics, the song is featured in all of Metallica's live albums and DVDs released after 1991 and has been played live at award ceremonies and benefit concerts.

"Enter Sandman" was the first song Metallica had written for their 1991 eponymous album, Metallica. Metallica's songwriting at that time was done mainly by rhythm guitarist James Hetfield and drummer Lars Ulrich, after they gathered tapes of song ideas and concepts from the other members of the band, lead guitarist Kirk Hammett and bassist Jason Newsted. Ulrich's house in Berkeley, California was used for this purpose. "Enter Sandman" evolved from a guitar riff that Hammett wrote. Originally, the riff was two bars in length, but Ulrich suggested the first bar be played three times. The instrumental parts of the song were quickly finished, but Hetfield did not come up with vocal melodies and lyrics for a long time. The song was among the album's last to have lyrics, and the lyrics featured in the song are not the original; Hetfield felt that "Enter Sandman" sounded "catchy and kind of commercial" and so to counterbalance the sound, he wrote lyrics about "destroy[ing] the perfect family; a huge horrible secret in a family" that included references to crib death. For the first time in Metallica's history, however, Ulrich and producer Bob Rock told Hetfield that they felt he could write better lyrics. Nevertheless, according to Ulrich, the song was the "foundation, the guide to the whole record" even before it had lyrics.

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