Twelfth Night, Or What You Will is a comedy by William Shakespeare, based on the short story "Of Apolonius and Silla" by Barnabe Rich. It is named after the Twelfth Night holiday of the Christmas season. It was written around 1601 and first published in the First Folio in 1623. The main title is believed to be an afterthought, created after John Marston premiered a play titled What You Will during the course of the writing.
— Excerpted from Wikipedia, the free encyclopedia.