The Woman in White is an epistolary novel written by Wilkie Collins in 1859, serialized in 1859–1860, and first published in book form in 1860. It is considered to be among the first mystery novels and is widely regarded as one of the first (and finest) in the genre of 'sensation novels'.

The story is considered an early example of detective fiction with the hero, Walter Hartright, employing many of the sleuthing techniques of later private detectives. The use of multiple narratives draws on Collins's legal training, and as he points out in his Preamble: 'the story here presented will be told by more than one pen, as the story of an offence against the laws is told in Court by more than one witness'. In 2003, Robert McCrum writing for The Observer listed The Woman in White number 23 in "the top 100 greatest novels of all time", and the novel was listed at number 77 on the BBC's survey The Big Read.

Walter Hartright, a young art teacher, is walking from Hampstead to London late one summer's evening, when he meets a mysterious woman dressed in white, apparently in deep distress. He helps her on her way to London, but later learns that she has escaped from an asylum. The next day he travels north to Limmeridge House, having been hired as a drawing master to the residents of the house; he had been recommended for the job by his friend, Pesca, an Italian language professor. The Limmeridge household comprises Mr Frederick Fairlie, and Walter's students: Laura Fairlie, Mr Fairlie's niece, and Marian Halcombe, her devoted half-sister. Several days after he arrives, Hartright is shocked to realize that Laura bears an astonishing resemblance to the woman in white, called Anne Catherick. The mentally disadvantaged Anne had lived for a time in Cumberland as a child and was devoted to Laura's mother, who first dressed her in white.

Walter and Laura quickly fall in love. Laura, however, has promised her father that she will marry Sir Percival Glyde, and Marian – knowing that Laura loves Walter in return – advises Walter to forget his love, and leave Limmeridge. Anne, after sending a letter to Laura warning her against Glyde, meets Hartright who becomes convinced that Glyde was responsible for shutting Anne in the asylum. Despite the misgivings of the Fairlie's lawyer over the financial terms of the marriage settlement, Laura and Glyde marry in December 1849 and travel to Italy for 6 months. Hartright also leaves England, joining an expedition to Honduras. After their honeymoon, Sir Percival and Lady Glyde return to his family estate, Blackwater Park, in Hampshire; they are accompanied by Glyde's friend, Count Fosco (who is married to Laura's aunt). Marian Halcombe is also living at Blackwater and learns that Glyde is in financial difficulties. Sir Percival unsuccessfully attempts to bully Laura into signing a document which would allow him to use her marriage settlement of £20,000. Determined to protect her sister, Marian crawls out onto a roof overlooking Percy and Fosco whilst they plot; but it begins to rain, and Marian, completely soaked, falls into a fever which shortly turns into typhus.

While Marian is ill, Laura is tricked into travelling to London. Her identity and that of Anne Catherick are then switched. Anne Catherick dies of a heart condition and is buried in Cumberland as Laura, while Laura is drugged and placed in the asylum as Anne Catherick. When Marian recovers and visits the asylum, hoping to learn something from Anne Catherick, she finds Laura, supposedly suffering from the delusion that she is Lady Glyde.

Marian bribes the nurse and Laura escapes. Hartright has safely returned from Honduras, and the three live together in obscure poverty, determined to restore Laura's identity. After some time Walter discovers Glyde's secret, which is that he was illegitimate, and therefore not entitled to inherit his parents' property. This secret was known only to Anne's mother, and while Anne never knew the secret, she spoke and acted as if she did. Many years earlier, Glyde had forged an entry in the marriage register at Old Welmingham Church to conceal his illegitimacy and hence unlawful inheritance of estate and title. Believing Walter either has discovered, or will discover his secret, Glyde attempts to destroy the register entry, but the church vestry catches fire and he perishes in the flames. Confronting Anne's mother, Hartright discovers that Anne was the illegitimate child of Laura's father, which accounts for their resemblance. On returning to London to resume his battle with Fosco, Hartright marries Laura. When he secretly tails Fosco to investigate him, Hartright also discovers that Fosco belongs to, and has betrayed, an Italian secret society (dubbed "The Brotherhood"), of which Pesca is a high-ranking member with enough authority to dispatch him. Using Fosco's weakness as bargaining chip, Hartright now has the power to force a written confession from Fosco and Laura's identity is restored. Fosco departs from England in haste, only to be discovered by the Brotherhood's agents some time later and murdered. Since Hartright and Laura have married, on the death of Frederick Fairlie, their son becomes the Heir of Limmeridge.