Harley Street is a street in Marylebone, Central London, named after Edward Harley, 2nd Earl of Oxford and Earl Mortimer and part of the Howard de Walden Estate. The nearest London Underground stations are Regent's Park, Great Portland Street and Oxford Circus. It is known for having a high concentration of doctors and medical practitioners.

It was already known as a wealthy locale by the time of Jane Austen's Sense and Sensibility (1813), in which she has the Dashwood sisters, Lucy Steele, Mrs Jennings, Edward Ferrars, and others spend some of their free time there while in London. It remained so later that century - in Elizabeth Gaskell's North and South (1854–55), Margaret Hale lived with her aunt Mrs. Shaw and cousin Edith in a house on Harley Street for nine years, before she moved with her parents to the fictional northern town of Milton, whilst in Henry James' The Turn of the Screw (1898), the wealthy uncle at the beginning of the work apparently has a house on Harley Street.

Many famous people have lived on Harley Street, including the Victorian Prime Minister William Ewart Gladstone, and the artist J. M. W. Turner. Queen's College, founded in 1848 and one of the oldest girls' schools in England, is situated on Harley Street.

Since the 19th century it has housed private specialists in medicine and surgery. This also drew it into London's criminal history in the form of the "Harley Street mystery", in which on 3 June 1880 the body of a 4ft 10 woman in her thirties was found in the basement of number 139 (then occupied by a merchant) in a barrel of chloride of lime - an inquest called Professor Augustus Pepper and Dr Frederick William Spurgin but she was never identified.

Since the 19th century the number of doctors, hospitals, and medical organisations in and around Harley Street has increased. Records show that there were around 20 doctors in 1860, 80 by 1900, and almost 200 by 1914. When the National Health Service was established in 1948, there were around 1,500. There are more than 3,000 people employed in the Harley Street area now, in clinics, medical and paramedical practices, and hospitals.

Those who have practised there include:

It was briefly alluded to in Arthur Conan Doyle's Sherlock Holmes adventure, Shoscombe Old Place. When a client, John Mason, came to call on Holmes at Baker Street, he confides in Holmes that his employer, Sir Robert Norberton, had gone mad. Holmes replies that this is Baker Street, not Harley Street, implying that Mason should go there for any complaints of madness, as they are far more equipped than he to deal with madness. As well, in The Adventure of the Devil's Foot, Dr Moore Agar of Harley Street is referenced, as having recommended Holmes to take a rest from his work in order to maintain his good health.

Harley Street has also been the home of other fictional medical professionals, such as Sir William Bradshaw in Virginia Woolf's Mrs. Dalloway (1925), the "nerve specialist" Sir Roderick Glossop in the novels of P.G. Wodehouse, a woman doctor in the novel Dr. Janet of Harley Street (1894) by Dr. Arabella Kenealy, and Dr. Jekyll at number 46 in the musical Jekyll & Hyde (musical). In the movie The Revenge of Frankenstein, Dr Victor Frankenstein aka Dr Franck after his brain transplant begins his medical practice on Harley Street W.^{[citation needed]}