Twelfth Night, or What You Will is a romantic comedy by William Shakespeare, believed to have been written around 1601–1602 as a Twelfth Night entertainment for the close of the Christmas season.

Viola, separated from her twin Sebastian, dresses as a boy and works for the Duke Orsino, whom she falls in love with. Orsino is in love with the Countess Olivia, and sends Viola to court her for him, but Olivia falls for Viola instead. Sebastian arrives, causing a flood of mistaken identity, and marries Olivia. Viola then reveals she is a girl and marries Orsino.