Vestas Feuer ("The Vestal Flame") is a fragment of an opera composed in 1803 by Ludwig van Beethoven to a libretto by Emanuel Schikaneder. The plot involves a romantic intrigue in which the heroine temporarily becomes a Vestal Virgin (a keeper of the Vestal Flame in Ancient Rome). Beethoven set to music only the first scene of Schikaneder's libretto, then abandoned the project. The fragment (about ten minutes of music) is rarely performed.

Emanuel Schikaneder (1751–1812) was not just a librettist but also an actor, singer, playwright, and theater director. He had already achieved a form of immortality in 1791 by authoring the libretto of (and generally sponsoring) Mozart's opera The Magic Flute, a tremendous success at its premiere and still an important part of his company's repertoire. According to Lockwood, The Magic Flute was an opera that Beethoven "loved ... and knew like the back of his hand". In 1801, Schikaneder's company had abandoned the Theater auf der Wieden in which The Magic Flute had premiered, and moved into a larger and grander theater he had built, the Theater an der Wien. This theater was well suited to Schikaneder's preference for theatrical spectacle, with elaborate scenery and stage effects. The theater opened with an opera about Alexander the Great, composed by Franz Teyber; the libretto had been offered by Schikaneder first to Beethoven, who had declined it.

By 1803, the year of his Beethoven collaboration, the 51-year-old Schikaneder was already seeing his career go into decline (ultimately, it collapsed entirely), but at the time he was still an important figure in the Viennese theatrical and musical scene. "Vestas Feuer" was his last libretto.

For Beethoven, 1803 was a pivotal year. He was 32, and during the eleven years he had spent in Vienna he had already established himself as a leading composer. He had recently begun an important shift in his compositional methods and goals, a shift that emphasized the musical portrayal of heroism and led to what today is often called his Middle Period. Already completed were important new works such as the Op. 31 piano sonatas, and on his desk were massive new works representing the Middle Period in full flower: the Waldstein Sonata and the Third Symphony.

Beethoven's collaboration with Schikaneder was only the latest in a series of experiences he had had since arriving in Vienna in 1792 paralleling the life experiences (patrons, colleagues, performing venues, travel itineraries) of Mozart, who had died in 1791; for discussion see Mozart and Beethoven.

During the years he spent at the Theater auf der Wieden, Schikaneder had found it efficient to live where he worked; i.e. in the same apartment complex that included the theater; many of his colleagues lived there too. Schikaneder made sure he could continue this practice by incorporating into the new Theater an der Wien a four-story apartment house where he and a number of members of his theatrical company dwelt.

In early 1803 Schikaneder made another attempt to collaborate with Beethoven: he asked him to compose an opera for his theater, providing as a partial incentive free housing in the apartment complex. Beethoven agreed and moved into the complex, where he was to live from about April 1803 to May 1804, apart from some summer visits (his custom) to nearby rural locations in Baden and Oberdöbling. Beethoven's younger brother Kaspar Karl, who was acting as his business manager at the time, also moved into one of the theater's apartments. Beethoven scheduled a concert of his works for the theater in April; and the theater was to continue as a favored venue for him.

At first Beethoven was free of any obligations in the collaboration, since Schikaneder did not finish his libretto for Beethoven until late October. Beethoven was in any event fully occupied with composing other works (see above). He began work on Vestas Feuer in late November and kept at it for about a month.