The Symphony No. 91 in E♭ major, Hoboken I/91, was written by Joseph Haydn. It was completed in 1788 as part of a three-symphony commission from Count d'Ogny for the Concert de la Loge Olympique,[1] a successor to Haydn's series of "Paris symphonies". It is occasionally referred to as The Letter T referring to an older method of cataloguing Haydn's symphonic output.[citation needed]This triptych also includes Haydn's own Symphony No. 90 and Symphony No. 92.[2]
The autograph manuscript bears a dedication to d'Ogny, but Haydn also gave Prince Krafft Ernst von Oettingen-Wallerstein a copy as if it were an original.[3]