The Symphony no. 91 in E flat major, Hoboken 1/91, was completed by Joseph Haydn in 1788 as part of a three-symphony commission by Comte d'Ogny for the Concerts de la Loge Olympique. It features a standard four movement form and it is scored for flute, two oboes, two bassoons, two horns, continuo (harpsichord) and strings. It is occasionally referred to as The Letter T referring to an older method of cataloguing Haydn's symphonic output. 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.
