A Study in Scarlet is a detective mystery novel written by Sir Arthur Conan Doyle, which was first published in 1887. It is the first story to feature the character of Sherlock Holmes, who would la...

A Study in Scarlet is a detective mystery novel written by Sir Arthur Conan Doyle, which was first published in 1887. It is the first story to feature the character of Sherlock Holmes, who would later become one of the most famous literary detective characters, with long-lasting interest and appeal. The book's title derives from a speech given by Holmes to his companion Doctor Watson on the nature of his work, in which he describes the story's murder investigation as his "study in scarlet": "There’s the scarlet thread of murder running through the colourless skein of life, and our duty is to unravel it, and isolate it, and expose every inch of it."

Conan Doyle wrote the novel at the age of 27 in less than three weeks. As a general practice doctor in Southsea, Portsmouth, he had already published short stories in several magazines of the day, such as the periodical London Society. The story was originally titled A Tangled Skein, and was eventually published by Ward Lock & Co. in Beeton's Christmas Annual 1887, after many rejections. The author received ￡25 in return for the full rights (although Conan Doyle had pressed for a royalty instead). It was illustrated by D. H. Friston. The novel was first published as a book on July 1888 by Ward, Lock & Co., and featured drawings by the author's father, Charles Doyle. A second edition appeared the following year and was illustrated by George Hutchinson; a year later in 1890, J. B. Lippincott & Co. released the first American version. Numerous further editions, translations and dramatisations have appeared since.

The story, and its main character, attracted little public interest when it first appeared. Only 11 complete copies of Beeton's Christmas Annual 1887 are known to exist now and they have considerable value. Although Conan Doyle wrote 56 short stories featuring Holmes, A Study in Scarlet is one of only four full-length novels in the original canon. The novel was followed by The Sign of Four, published in 1890. A Study in Scarlet was the first work of fiction to incorporate the magnifying glass as an investigative tool.