Twelfth Night was written possibly as early as 1599, but is usually dated 1601. The earliest performance recorded is dated February 2, 1602 at the Middle Temple. Witness John Manningham observed that the play was "much like the Commedy of Errores, or Menechimi in Plautus, but most like and neere to that in Italian called Inganni." Shakespeare was most likely informed by at least three Italian plays titled GI'Inganni, ("The Frauds") which also utilize theme of mistaken identity. One of these Italian plays, written by Cuzio Gonzaga in 1592, even includes a character name "Cesare" or Cesario. However, the plot of Twelfth Night seems to be derived mainly from the story "Apolonius and Silla" by Barnaby Riche, in his Riche, His Farewell to the Military Profession, (1581), which in turn was based on another Italian comedy GI'Ingannati ("The Deceived"), first acted in 1531. Matteo Bandello's 1554 Novelle, translated into French by Francois de Belleforest in his 1579 Histoires tragiques, is another version of this story. Twelfth Night also shares similarities with other plays within the Shakespeare canon: The Comedy of Errors also includes identical twins, and The Two Gentlemen of Verona includes the theme of a girl dressed as a page, who must woo another woman for the man she loves.

Written most likely after his other comedies Much Ado About Nothing and As You Like It, and before the great tragedies Hamlet, Macbeth, and King Lear, many critics agree that Shakespeare reached his comic peak with this play, praising him for his nearly perfect construction and comedic form in Twelfth Night. Nineteenth-century critic William Hazlitt wrote that "this is Justly considered as one of the most delightful of Shakespeare's comedies," and twentieth century director and critic Harley Granville-Barker called Twelfth Night "the last play of Shakespeare's golden age."

Twelfth Night explores a variety of themes and issues. The major theme of celebration and festivity was prevalent in all of the sources from which Shakespeare drew. Critics have explored the impact of this theme on the play's events as well as the limitations of celebration. The conflict between appearance and reality is brought to the fore by die elements of role-playing and disguise. Additionally, the use of language to deceive as well as the failure of characters to communicate effectively or truthfully are also issues studied and debated among critics and students of the play.