Produced by Hartswood Films, the new series will return with three brand-new episodes promising "laughter, tears, shocks, surprises and extraordinary cases".
We'll see Sherlock back on British soil, while Doctor Watson and his wife Mary prepare for their biggest ever challenge - becoming parents for the first time.
Star of the show Benedict Cumberbatch said he was "genuinely thrilled to be back filming Sherlock with all the cast and crew. I can't wait for everyone to see season four. But you will have to wait… though not for long... And it will be worth it."
The last time we saw Sherlock on screen was The Abominable Bride, which aired on New Year's Day.
Co-creators Steven Moffat and Mark Gatiss, said: "Sherlock series four - here we go again! Whatever else we do, wherever we all go, all roads lead back to Baker Street - and it always feels like coming home.
"Ghosts of the past are rising in the lives of Sherlock Holmes and John Watson bringing adventure, romance and terror in their wake. This is the story we've been telling from the beginning. A story about to reach its climax..."
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