The Baker Street Irregulars is a gang of young street children whom Sherlock Holmes often employs to aid his cases. They first appeared in Conan Doyle's first novel, A Study in Scarlet. They also appear in The Sign of the Four, one of the chapters from the novel is titled "The Baker Street Irregulars".
The head of the group is called Wiggins. Holmes pays them a shilling a day (plus expenses), with a guinea prize (worth one pound and one shilling) for a vital clue.
- The Special Operations Executive (SOE), tasked by Winston Churchill to "Set Europe ablaze" during World War II had their headquarters at 64 Baker Street and were often called the Baker Street Irregulars after Sherlock Holmes's fictional group of boys employed "to go everywhere, see everything, and overhear everyone," as they spied about London.
- The Baker Street Irregulars is a society of Sherlock Holmes enthusiasts that was founded in 1934.
- The Irregulars appear as the main characters in Sherlock Holmes and the Baker Street Irregulars: The Fall of the Amazing Zalindas, a 2006 novel by Tracy Mack and Michael Citrin. Wiggins is again the leader of a gang of street urchins. Other major characters include Ozzie, a scrivener's apprentice; Rohan, an Indian boy; Elliot, from an Irish tailor's family; Pilar, a Gypsy girl; and little Alfie. The Irregulars help solve the mysterious deaths of three tightrope walkers at a circus.
- Hazel Meade's troop of children serve as couriers and lookouts in the "Baker Street Irregulars" during the lunar revolution of Robert A. Heinlein's The Moon is a Harsh Mistress (1966).
- Two BBC television series have been made starring the Irregulars: The Baker Street Boys (1983) and Sherlock Holmes and the Baker Street Irregulars (2007).
- Comics involving the Irregulars include The Irregulars from Dark Horse Comics, and The Baker Street Four (Les Quatre de Baker Street in its native French).
- In June 2010 it was announced that Franklin Watts books, a part of Hachette Children's Books planned to release a series of four children's graphic novels in spring 2011 called Sherlock Holmes: The Baker Street Irregulars set during the three years that Sherlock Holmes was believed dead, between The Adventure of the Final Problem and The Adventure of the Empty House by writer Tony Lee and artist Dan Boultwood.
- In the BBC modern adaptation Sherlock, Holmes uses a wide network of homeless people as an information network.
- In the CBS modern adaptation Elementary, Holmes uses Teddy and his crew of street venders as informants to help him track down M. In the course of the series, another group of 'Irregulars' are introduced in the form of experts Holmes consults when he requires more specialist knowledge of a case-related subject than his own expertise. Members of this network include mathematician Harlan Emple, a meteorologist, Mrs Hudson (an expert in Greek literature who acts as a 'muse' for wealthy men) and a man with a particularly keen sense of smell.