He made the announcement on Radio 2, and it has sent fans into meltdown as rumours begin to swirl over who his replacement will be.
Ben Whishaw is right up there in the running, and you may remember him as Q from the recent James Bond films.
He would be my number one choice. He’s a very versatile actor, and I think he would have the emotional range that the role demands, as well as that quirkiness which always makes for a good Doctor.
There are also calls for the next Doctor to be a woman, which would be a very interesting shift.
There is certainly no reason why the Doctor should be a man all the time, and the fantastic Olivia Colman is a better candidate than a lot of the men who will be put forward for the role. Colman worked with incoming Doctor Who writer Chris Chibnall on Broadchurch, so she could be a good outside bet.
Capaldi was the 12th actor to play the iconic role, and he was also the oldest.
He was best known for the part he played as Malcolm Tucker in The Thick of It, and he will be missed by the current generation of Doctor Who fans.
He will still play The Doctor in the upcoming series and the Christmas special, so there is plenty of time to watch Capaldi as The Doctor still.
Unbelievably, Capaldi began as the Doctor in 2013 (it only seems like two minutes ago that he became the Doctor!) so he will have been in the role for four years by the time he leaves, which is a good chunk of time for an actor to spend as one character.
The episodes where there is a re-generation are usually the best as viewers discover who the next Doctor is, so that Christmas special promises to be a cracker.