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

As London prepares for Christmas, newspapers report the theft of a near-priceless gemstone, the "Blue Carbuncle", from the Countess of Morcar's hotel suite. The police arrest John Horner, a plumber with a criminal record who was in the Countess's room repairing a fireplace grate.

Meanwhile, at 221B Baker Street, Dr Watson finds Sherlock Holmes contemplating a battered old hat brought to him by Peterson, a commissionaire who seeks Holmes's help in returning it and a Christmas goose to their rightful owners after he found them the previous night in the street after a scuffle. A tag on the goose reading "For Mrs Henry Baker" is of little assistance, as the name is a very common one. Ultimately, Peterson takes the goose home for dinner and Holmes keeps the hat to study as an intellectual exercise, deducing Baker's age, social standing, intellect, and domestic status.

An excited Peterson bursts in, having found the stolen gem in the goose's crop. That evening when Baker appears in response to advertisements placed by Holmes in the London newspapers, Holmes returns his hat and offers him a new goose. Happily accepting the replacement bird, Baker refuses the original bird's entrails, convincing Holmes that he knew nothing about the gem and that he had innocently purchased the goose, as he says, at the Alpha Inn, a pub near the British Museum.

Holmes and Watson visit the pub, where the proprietor informs them that the bird had been purchased from a Covent Garden dealer. However, the latter refuses to help, complaining that he has been repeatedly pestered by another man about geese purchased by the Alpha Inn. Realising that he is not the only one aware of the goose's importance, Holmes tricks the dealer into revealing that the bird was supplied to him by its breeder, a Mrs Oakshott of Brixton. The dealer's other "pesterer" re-appears – it is James Ryder, head attendant of the hotel where the gem had been stolen.

After being confronted with the jewel back at Baker Street, a remorseful Ryder admits that he and his accomplice, the Countess's maid, had contrived to frame Horner, as his criminal past would make him an easy scapegoat. During a visit to his sister, Mrs Oakshott, Ryder had concealed the gem by feeding it to a goose she had promised him as a gift, but confused the bird with another. By the time he realised his mistake, his goose had already been sold. As it is Christmas, Holmes takes pity on Ryder and allows him to leave, concluding that the man is too frightened by what happened to offend again. Holmes is confident that Horner will be freed once the case against him collapses.

"The Adventure of the Blue Carbuncle" was first published with eight illustrations by Sidney Paget in The Strand Magazine in January 1892, and in the US edition of the Strand in February 1892. It was also included in the short story collection The Adventures of Sherlock Holmes published in October 1892.

A silent short film based on the story was released in 1923 as part of the Stoll film series starring Eille Norwood as Sherlock Holmes.