Demon Days is the second studio album by the supergroup Gorillaz, first released in May 2005. It is the band's first studio album of new material since their self-titled debut album Gorillaz. The album features contributions from De La Soul, Neneh Cherry, Martina Topley-Bird, Roots Manuva, MF Doom, Ike Turner, Bootie Brown of the Pharcyde, Shaun Ryder, Dennis Hopper, the London Community Gospel Choir and the Children's Choir of San Fernandez.

Demon Days entered the UK charts at #1 and the US charts at #6, outperforming their 2001 debut, while lead single "Feel Good Inc." became their biggest hit (UK #2, US #14) at the time. The second single "DARE" featured Shaun Ryder and became a huge hit, and also became their 1st UK No.1 .

The album was first mentioned in articles detailing the reopening of the Gorillaz' website on December 8, 2004. At first a March or April 2005 release date was announced but later pushed back to the date it was finally released. In an article for Q magazine in February 2005 it was reported that the album was to be titled We Are Happy Landfill. Another early title was reported to be Reject False Icons, which is also the title of Gorillaz' culture jamming project.