13 Reasons Why (stylized onscreen as Th1rteen R3asons Why) is an American drama-mystery web television series based on the 2007 novel Thirteen Reasons Why by Jay Asher and adapted by Brian Yorkey for Netflix. The series revolves around a high school student, Clay Jensen, and his friend Hannah Baker, a girl who committed suicide after suffering a series of demoralizing circumstances brought on by select individuals at her school. A box of cassette tapes recorded by Hannah before her suicide details thirteen reasons why she ended her life.

Diana Son and Brian Yorkey serve as showrunners on the series. The first season consists of thirteen episodes. The series is produced by July Moon Productions, Kicked to the Curb Productions, Anonymous Content, and Paramount Television. Originally conceived as a film set to be released by Universal Pictures with Selena Gomez in the lead role, the adaptation was picked up as a television series by Netflix in late 2015. Gomez serves as an executive producer. The first season, and the special 13 Reasons Why: Beyond the Reasons, were released worldwide on Netflix on March 31, 2017.

The series has received largely positive reviews from critics and audiences, who have praised its subject matter and casting, particularly the two leads, Dylan Minnette and Katherine Langford. It has attracted controversy from some over the series' graphic depiction of issues such as suicide and rape, along with other mature content. In May 2017, it was announced that the series had been renewed for a second season, scheduled to premiere in 2018.