Torchwood: Miracle Day is the fourth and final series of the British science fiction television programme Torchwood, a spin-off from the long-running show Doctor Who. In contrast to the first three series, which were produced by the BBC, the fourth series was a British–American co-production involving the BBC's drama production house BBC Cymru Wales for BBC Worldwide and the US premium network Starz. It was broadcast in ten episodes beginning on 8 July 2011 (U.S.) and 14 July 2011 (UK).

Torchwood is a British science fiction television programme created by Russell T Davies. A spin-off of the 2005 revival of Doctor Who, it aired from 2006 to 2011. The show shifted its broadcast channel each series to reflect its growing audience, moving from BBC Three to BBC Two to BBC One, and acquiring American financing in its fourth series when it became a co-production of BBC One and Starz. Torchwood is aimed at adults and older teenagers, in contrast to Doctor Who's target audience of both adults and children. As well as science fiction, the show explores a number of themes, including existentialism, LGBTQ+ sexuality, and human corruptibility.