The Fantasticks is a musical with music by Harvey Schmidt and lyrics and a book by Tom Jones, loosely based on the 1894 play Les Romanesques by Edmond Rostand. It tells an allegorical story concerning two neighboring fathers who trick their children into falling in love by pretending to feud.

The show's original off-Broadway production ran a total of 42 years (until 2002) and 17,162 performances, making it the world's longest-running musical. The musical was produced by Lore Noto. It was awarded Tony Honors for Excellence in Theatre in 1991. The poetic book and breezy, inventive score, including such memorable songs as "Try to Remember", helped make the show durable. Many productions followed, as well as television and film versions. The Fantasticks has become a staple of regional, community and high school productions since its premiere, with approximately 250 new productions each year. It is played with a small cast, two- to three-person orchestra and minimalist set design.

The show was revived off Broadway from 2006 to 2017. As of 2010, its original investors had earned 240 times their original investments. The musical has played in all 50 US states and in at least 67 foreign countries.

The 1954 Marc Blitzstein adaptation of The Threepenny Opera, which ran for six years, showed that musicals could be profitable off-Broadway in a small-scale, small orchestra format. This was confirmed in 1959 when a revival of Jerome Kern and P. G. Wodehouse's Leave It to Jane ran for more than two years. The 1959–1960 off-Broadway season included a dozen musicals and revues including Little Mary Sunshine, The Fantasticks, and Ernest in Love, a musicalization of Oscar Wilde's 1895 hit The Importance of Being Earnest.

The musical is based loosely on The Romancers (Les Romanesques) by Edmond Rostand, which draws elements from the story of Pyramus and Thisbe, Shakespeare's Romeo and Juliet and A Midsummer Night's Dream, and Donizetti's L'elisir d'amore.

Jones, together with John Donald Robb of the University of New Mexico, first adapted the Rostand play as a Western titled Joy Comes to Deadhorse. The play premiered at the University of New Mexico in the spring of 1956. It was set in the American West, and featured a "half-breed Apache" among the characters. Jones was not happy with this version and subsequently teamed with Schmidt.

The script was substantially rewritten by Jones and Schmidt, with the character of Mortimer now "not really an Indian" but playing one during the "Rape Ballet" sequence. The Wild West setting was abandoned, as was most of the script. All but a few songs in the score were also jettisoned, and the staging of the play was changed to a thrust stage. Tom Jones says that the name of the play came from George Fleming's 1900 adaptation of the Rostand play, which used the name The Fantasticks. Harley Granville-Barker's book, On Dramatic Method, provided the idea of using a series of images to help weave a unifying theme to the play. Thornton Wilder's Our Town gave Jones the idea of using a narrator, the staging of Carlo Goldoni's Servant of Two Masters provided the concept of having actors sit stage-side when not acting, and John Houseman's production of The Winter's Tale and Leonard Bernstein's Candide suggested the use of sun, moon, frozen action, and incidental music. The song "Try to Remember" was added at this time. Harvey Schmidt says he wrote it in a single afternoon, after it emerged in almost complete form after a fruitless afternoon attempting to compose other songs.

The revamped play appeared on a bill of new one-act plays at Barnard College for one week in August 1959.