Sherlock Holmes is a fictional detective of the late 19th and early 20th century, created by British author and physician Arthur Conan Doyle. He is famous for his prowess at using logic and careful observation to solve cases.

Holmes was said to have lived at 221B Baker Street (an upper-storey flat at 221 Baker Street; in early notes it was described as Upper Baker Street), where he spent many of his professional years with his friend and colleague Dr. Watson while the residence was maintained by Mrs. Hudson.

Sherlock Holmes describes himself as a "consulting detective", which means that he is brought into cases that have proven too difficult for other investigators; we are told that he is often able to solve a problem without leaving home (although this aspect is somewhat lost in the stories themselves, which focus on the more interesting cases which often do require him to do actual legwork). He specializes in solving unusual cases using his extraordinary powers of observation and "deduction".

Sir Arthur Conan Doyle credits the inception of Holmes on his teacher at the medical school of Edinburgh University, the gifted surgeon and forensic detective Joseph Bell, forensic science being a new type of science at the time. However, some years later Bell wrote to Conan Doyle: "you are yourself Sherlock Holmes and well you know it" (Baring-Gould, p. 8). The 'Sherlock Holmes' name was derived from a pair of cricketers – however some early notes give his name as Sherrinford Holmes.

It is a popular myth that Sherlock Holmes gave rise to the entire genre of murder mystery fiction; in reality, the detective genre was alive before Holmes, if not one which followed a logical progression to the solution. Many fictional detectives have imitated Holmes' logical methods and followed in his footsteps, in many different ways. Some of the more popular fictional detectives to continue Holmes' legacy include Agatha Christie's Hercule Poirot, Ellery Queen, Perry Mason, Columbo, Dick Tracy, and even the comic book superhero Batman. A modern variant might be the NBC series TV show Law and Order: Criminal Intent.