№ 4 (sometimes referred to as No. 4) is the fourth album released by Stone Temple Pilots, on October 26, 1999, by Atlantic Records. The album was a return to the band's earlier hard rock roots, while also blending elements of heavy metal, psychedelic rock, and alternative rock. Despite the lack of promotion due to singer Scott Weiland's one-year jail sentence shortly before the album's release, No. 4 was certified Platinum by the RIAA on August 7, 2000, and by the CRIA in August 2001. The song "Down" was nominated for Best Hard Rock Performance at the Grammy Awards. The album also produced one of STP's biggest hits, "Sour Girl", which charted at #78 on the Hot 100, their only song to appear on that chart. The CD was originally released as a digipak, then later changed to a standard jewel case.
No.4 displays a deliberate effort by the band to return to a more hard rock-oriented sound featured on its first two albums. Allmusic cited the album as STP's "hardest effort" since Core, remarking that "it's as if STP decided to compete directly with the new generation of alt-metal bands who prize aggression over hooks or riffs." Stephen Erlewine also wrote that No.4 "consolidates all [of STP's] strengths."