Twilight (stylized as twilight) is a 2005 young adult vampire-romance novel by author Stephenie Meyer. It is the first book in the Twilight series, and introduces seventeen-year-old Isabella "Bella" Swan, who moves from Phoenix, Arizona to Forks, Washington. She is endangered after falling in love with Edward Cullen, a 103-year-old vampire frozen in his 17-year-old body. Additional novels in the series are New Moon, Eclipse, and Breaking Dawn.

Twilight received lukewarm reviews. Some praised the novel's tone and its portrayal of common teenage emotions such as alienation and rebellion. Others criticized Meyer's prose and argued the story was lacking in character development. It reached number five on the New York Times bestseller list within a month of its release and eventually reached first place. The novel was named one of Publishers Weekly's Best Children's Books of 2005.

The film adaptation, released in 2008, was a commercial success, grossing more than $392 million worldwide and making an additional $157 million in North American DVD sales as of July 2009. The book was the biggest-selling of 2008; in 2009, it was the second-biggest selling, losing only to its sequel New Moon. As of 2008, Twilight had been translated into 37 different languages.

In October 2015, Stephenie Meyer announced a new gender-swapped version of the novel, entitled Life and Death: Twilight Reimagined, with characters Beau and Edythe, in honor of the 10th anniversary of The Twilight Saga. In 2020, Meyer released Midnight Sun, a retelling of the story of Twilight from the perspective of Edward Cullen.