A Study in Scarlet is the original title of the novel A Study in Red (1887), by the Scottish writer Arthur Conan Doyle, in which the character of Sherlock Holmes makes his debut.
The novel first appeared in Beeton's Christmas Annual magazine alongside stories by other authors, while in 1888 it was republished as a standalone book. It was the first work of detective fiction in which the magnifying glass appears as an investigative tool.