Sherlock Holmes is such a popular character that there have been many theatrical stage, cinematic, television, novel, short story, comic book, graphic novel and even computer game adaptations of Conan Doyle's work over the years, much in the same way that Hamlet or Dracula are often revised and adapted.
Related and derivative works (non-canonical)
In addition to the canonical Sherlock Holmes stories, Conan Doyle's "The Lost Special" (1908) features an unnamed "amateur reasoner" clearly intended to be identified as Holmes by his readers. His explanation for a baffling disappearance, argued in Holmes' characteristic style, turns out to be quite wrong evidently Conan Doyle was not above poking fun at his own hero. A short story by Conan Doyle using the same idea is "The Man with the Watches". Another example of Conan Doyle's humor is "How Watson Learned the Trick" (1924), a parody of the frequent Watson-Holmes breakfast table scenes. A further parody by Conan Doyle is "The Field Bazaar". He also wrote other material, especially plays, featuring Holmes. Many of these writings are collected in the books Sherlock Holmes: the Published Apocrypha edited by Jack Tracy, The Final Adventures of Sherlock Holmes edited by Peter Haining and The Uncollected Sherlock Holmes compiled by Roger Lancelyn Green.
Sherlock Holmes' abilities as both a good fighter and as an excellent logician have been a boon to other authors who have lifted his name, or details of his exploits, for their plots. These range from Holmes as a cocaine addict, whose drug-fuelled fantasies lead him to cast an innocent Professor Moriarty as a supervillain (The Seven Per-Cent Solution), to science-fiction plots involving him being re-animated after death to fight crime in the future (Sherlock Holmes in the 22nd Century). Challenged to create a comedy about Sherlock Holmes, filmmaker Gene Wilder wrote, directed and starred in The Adventure of Sherlock Holmes' Smarter Brother.
Some authors have supplied stories to fit the tantalizing references in the canon to unpublished cases (e.g. "The giant rat of Sumatra, a story for which the world is not yet prepared" in "The Adventure of the Sussex Vampire"), notably The Exploits of Sherlock Holmes by Doyle's son Adrian Conan Doyle with John Dickson Carr; others have used different characters from the stories as their own detective, e.g. Mycroft Holmes in Enter the Lion by Michael P. Hodel and Sean M. Wright (1979) or Dr James Mortimer (from The Hound of the Baskervilles) in books by Gerard Williams.
A common setting for uncanonical pieces pits Holmes and Watson against the Nazis. Most notable were the films made during the Second World War starring Basil Rathbone, but more recently The Curse of the Nibelung: A Sherlock Holmes Mystery. Such pieces were in the spirit of Conan Doyle's patriotism, and indeed the canonic "His Last Bow" describes Holmes and his connections with British Intelligence on the eve of the First World War.
In 2006, best-selling author and military historian Caleb Carr (perhaps best known for The Alienist and The Angel of Darkness, both featuring Holmes-reminiscent protagonist Laszlo Kreizler) penned The Italian Secretary, a "continuing adventure of Sherlock Holmes." Dr John Watson and Mycroft Holmes play significant parts in this story, and other follow-on/related works (including, but not limited to, a Holmes/Kreizler crossover) may be forthcoming.
It is also common for writers to pit Holmes against other well-known fictional characters originating from or set in the same era as Conan Doyle's stories; particularly those who now exist in the public domain, and so can be used freely without payment of royalties to the creator. In these fictional crossovers, Holmes has frequently interacted with Dr Fu Manchu (in Cay Van Ash's Ten Years Beyond Baker Street), Doctor Jekyll and Mister Hyde (in Loren Eastman's Dr Jekyll and Mr Holmes) and Dracula (In Loren Eastman's Sherlock Holmes vs. Dracula or Stephen Seitz's "Sherlock Holmes and the Plague of Dracula"). He has also appeared as a significant (although often unseen) background presence in Alan Moore and Kevin O'Neill's comic book series The League of Extraordinary Gentlemen, and also Planetary by Warren Ellis.
Other writers have Holmes meeting real people and participating in real events. In Nicholas Meyer's works, Holmes meets Sigmund Freud, Oscar Wilde, Gilbert and Sullivan, and Bram Stoker, among other Victorian celebrities. In Sherlock Holmes and the Red Demon, Minnesota journalist Larry Millett involves Holmes and Watson in the Great Hinckley Fire; their employer is railroad magnate James J. Hill, and they also meet Boston Corbett, the man who shot John Wilkes Booth. And on at least six occasions (Edward B. Hanna's novel The Whitechapel Horrors, Michael Didbin's novel The Last Sherlock Holmes Story, Philip J. Carraher's novel The Adventure of the New York Ripper [with Holmes using the alias Simon Hawkes], Barry Day's novel Sherlock Holmes and the Apocalypse Murders, and the movies A Study in Terror and Murder by Decree) Holmes gets involved in the Jack the Ripper case. In Caitlín R. Kiernan's "The Drowned Geologist", Holmes is placed in Whitby at the same time as the stranding of the Demeter, the ship which carried Dracula to England.
In recent years, Holmes has been featured in the Mary Russell series, by Laurie R. King. In the books Holmes is married to Mary Russell, a woman thirty-nine years his junior, and makes her his partner in detection. Carole Nelson Douglas also wrote an eight-novel detective series starring Irene Adler as a detective that also features Holmes.