A Wind in the Door is a fantasy novel in the Time Quintet series by Madeleine L'Engle. It was published on January 1st, 1973, by Farrar, Straus, and Giroux. It is a companion book to L'Engle's 1963 novel, A Wrinkle in Time. It is followed by its sequel, A Swiftly Tilting Planet.
The novel includes the same characters as A Wrinkle in Time, though it is not a sequel. It began as a short story titled Intergalactic P.S. 3. The short story was published as a pamphlet in 1970. During the following three years, the concept expanded into a 240 page novel.
A Wind in the Door received mostly positive reviews upon release. It was praised in The School Library Journal as "complex and rich" and a "breathtaking environment." In 1978, it received the Learning A-V Award.