Haydn composed his Symphony in B-flat Major, Hob. I:66 between 1775 and 1776, around ten years after taking up his post at the Esterházy Palace. At this time, the opera activities at the court were in a phase of development and the prince's chapel was expanded for opera productions. Thus Haydn was able to employ two bassoon parts for the first time in the symphonies written during that time, thereby creating a fuller sound in the woodwind section of Symphony No. 66. Musically, this symphony is characterised by its operatic character, which corresponded to the general musical taste of the time. This is particularly noticeable in the finale "Scherzando e presto", whose playful, irregularly structured rondo theme juxtaposes contrasting compositional techniques to great effect and foreshadows Haydn's late symphonic work.