Friedrich Wilhelm Jähns (German: [jɛːns]; 2 January 1809 – 8 August 1888) was a German music scholar, voice teacher, and composer. He is best known for his chronological catalog of the works of Carl Maria von Weber.
Jähns was born and died in Berlin. His grave is preserved in the Protestant Friedhof I der Jerusalems- und Neuen Kirchengemeinde (Cemetery No. I of the congregations of Jerusalem's Church and New Church) in Berlin-Kreuzberg, south of Hallesches Tor.
Der Freischütz (J. 277, Op. 77 The Marksman or The Freeshooter) is a German opera with spoken dialogue in three acts by Carl Maria von Weber with a libretto by Friedrich Kind, based on a story by Johann August Apel and Friedrich Laun from their 1810 collection Gespensterbuch. It premiered on 18 June 1821 at the Schauspielhaus Berlin. It is considered the first German Romantic opera.
The opera's plot is mainly based on August Apel's tale "Der Freischütz" from the Gespensterbuch though the hermit, Kaspar and Ännchen are new to Kind's libretto. That Weber's tunes were just German folk music is a common misconception. Its unearthly portrayal of the supernatural in the famous Wolf's Glen scene has been described as "the most expressive rendering of the gruesome that is to be found in a musical score".