Hybrid Theory is the debut studio album by American rock band Linkin Park, released on October 24, 2000, by Warner Bros. Records. Recorded at NRG Recordings in North Hollywood, California, and produced by Don Gilmore, the album's lyrical themes deal with problems lead vocalist Chester Bennington experienced during his adolescence, including drug abuse and the constant fighting and eventual divorce of his parents. Hybrid Theory takes its title from the previous name of the band as well as the concepts of music theory and combining different styles. It is also the band's only album in which bassist Dave "Phoenix" Farrell does not play, however, he is credited as a member of the band as well as a songwriter on some of its tracks.

Four singles were released from Hybrid Theory: "One Step Closer", "In the End", "Crawling" and "Papercut", all of them being responsible for launching Linkin Park into mainstream popularity. While "In the End" was the most successful of the four, all of the singles in the album remain some of the band's most successful songs to date. Although "Runaway", "Points of Authority", and "My December" from the special edition bonus disc album were not released as singles, they were minor hits on alternative rock radio stations thanks to the success of all of the band's singles and the album.

Generally receiving positive reviews from critics upon its release, Hybrid Theory became a strong commercial success. Peaking at number two on the US Billboard 200, it is certified 12× Platinum by the Recording Industry Association of America (RIAA). It also reached the top 10 in 15 other countries and has sold 32 million copies worldwide, making it the best-selling debut album since Guns N' Roses's Appetite for Destruction (1987). At the 44th Grammy Awards, it won Best Hard Rock Performance for "Crawling".

On August 13, 2020, Warner Records announced a re-release of Hybrid Theory for its 20th anniversary. A previously unreleased demo song, "She Couldn't", was released at the same time.