"The Christmas Invasion" is a 60-minute special episode of the British science fiction television programme Doctor Who, first broadcast on BBC One on 25 December 2005. This episode features the first full-episode appearance of David Tennant as the Doctor. It is also the first specially produced Christmas special in the programme's history, commissioned following the success of the first series earlier in the year, to see how well the show could do at Christmas. It was written by showrunner and executive producer Russell T Davies and was directed by James Hawes.

In the episode, principally set in London, the newly regenerated Tenth Doctor is out of action, leaving Rose, Mickey and Jackie to combat the invasion of an alien race known as the Sycorax. The Sycorax demand that either humanity have to surrender half of themselves as slaves or one third of them will die through the Sycorax's blood control.

"The Christmas Invasion" was watched by 9.84 million viewers, the highest-rated episode of the Tenth Doctor, up until the "Voyage of the Damned", which achieved an audience of 13.31 million viewers. The episode received positive reviews from critics, who welcomed Tennant to the show, and is considered one of the best Christmas specials of the show, with its success leading to the Christmas special becoming an annual tradition.