"The Adventure of the Blue Carbuncle" is one of 56 short Sherlock Holmes stories written by British author Sir Arthur Conan Doyle, the seventh story of twelve in the collection The Adventures of Sherlock Holmes. It was first published in Strand Magazine in January 1892.

As London prepares for Christmas, newspapers report the theft of the near priceless jewel, the "Blue Carbuncle", from the hotel suite of the Countess of Morcar. John Horner, a plumber and a previously convicted felon, is soon arrested for the theft. Though the police have yet to find the jewel, and despite Horner's claims of innocence, the police are sure that they have the thief. Horner's record, and his presence in the Countess's room where he was repairing a fireplace, are all the police need.