Franz Schubert's Symphony No. 8 in B minor, D. 759 (sometimes renumbered as Symphony No. 7, in accordance with the revised Deutsch catalogue and the Neue Schubert-Ausgabe), commonly known as the Unfinished Symphony (German: Unvollendete), is a musical composition that Schubert started in 1822 but left with only two movements—though he lived for another six years. A scherzo, nearly completed in piano score but with only two pages orchestrated, also survives.

It has been theorized by some musicologists, including Brian Newbould, that Schubert may have sketched a finale that instead became the big B minor entr'acte from his incidental music to Rosamunde, but all evidence for this is circumstantial. One possible reason for Schubert's leaving the symphony incomplete is the predominance of the same meter (triple meter). The first movement is in 34, the second in 38 and the third (an incomplete scherzo) again in 34. Three consecutive movements in basically the same meter rarely occur in symphonies, sonatas, or chamber works of the most important Viennese composers.

Schubert's Eighth Symphony is sometimes called the first Romantic symphony due to its emphasis on the lyrical impulse within the dramatic structure of Classical sonata form. Furthermore, its orchestration is not solely tailored for functionality, but specific combinations of instrumental timbre that are prophetic of the later Romantic movement, with astonishing vertical spacing occurring for example at the beginning of the development.To this day, musicologists still disagree as to why Schubert failed to complete the symphony. Some have speculated that he stopped work in the middle of the scherzo in the fall of 1822 because he associated it with his initial outbreak of syphilis—or that he was distracted by the inspiration for his Wanderer Fantasy for solo piano, which occupied his time and energy immediately afterward. It could have been a combination of both factors.