The Earth Tour: 21 Nights in London was a concert residency at the O2 arena in London by American recording artist Prince that commenced on 1 August 2007 and concluded on 21 September 2007.

[1] It was nominally in support of his recently released Planet Earth album which had been distributed in the UK for free with copies of The Mail on Sunday newspaper on 15 July 2007,[2] although the performances themselves primarily concentrated on earlier hits.

Tickets for the concerts were priced at £31.21, echoing the title of Prince's 2006 album 3121.

[1][3] The concerts were followed by an after-party held at the neighbouring IndigO2 venue, also housed within the O2 facility, and which often saw Prince continue to perform, although these appearances were not guaranteed.

[1][3] The Earth Tour remains the longest residency to have been held at the venue.