The Curious Incident of the Dog in the Night-Time is a 2003 mystery novel by British writer Mark Haddon. Haddon and The Curious Incident won the Whitbread Book Awards for Best Novel and Book of the Year, the Commonwealth Writers' Prize for Best First Book, and the Guardian Children's Fiction Prize.

Haddon considered this his first novel for adults, as his previous books were for children. Unusually, his publisher also released a separate edition for the children's market, and it was successful there.

The novel is narrated in the first-person by Christopher John Francis Boone, a 15-year-old boy who is described as "a mathematician with some behavioural difficulties" living in Swindon, Wiltshire. Although Christopher's condition is not stated, the book's blurb refers to Asperger syndrome. Some commentators have characterized Christopher as on the autism spectrum.

In July 2009, Haddon wrote on his blog that "The Curious Incident is not a book about Asperger's ... if anything it's a novel about difference, about being an outsider, about seeing the world in a surprising and revealing way. The protagonist, being neuro-diverse shows that. The book is not specifically about any specific disorder". Haddon said that he is not an expert on the autism spectrum or Asperger's syndrome.

He chose to indicate chapters by prime numbers, rather than the conventional successive numbers, to express a different world view. Originally written in English, the book has been translated into 36 additional languages.

The book’s title is a line of Sherlock Holmes’ dialogue from the short story, "The Adventure of Silver Blaze" by Sir Arthur Conan Doyle.