Franz Joseph Haydn ( HY-dən; German: [ˈfʁants ˈjoːzɛf ˈhaɪdn̩] ; 31 March 1732 – 31 May 1809) was an Austrian composer of the Classical period. He was instrumental in the development of chamber music such as the string quartet and piano trio. His contributions to musical form have led him to be called "Father of the Symphony" and "Father of the String quartet".

Haydn arose from humble origins, the child of working people in a rural village. He established his career first by serving as a chorister at St. Stephen's Cathedral, Vienna, then through an arduous period as a freelance musician. Eventually he found career success, spending much of his working life as music director for the wealthy Esterházy family at their palace of Eszterháza in rural Hungary. Though he had his own orchestra there, it isolated him from other composers and trends in music so that he was, as he put it, "forced to become original". During this period his music circulated widely in publication, eventually making him the most celebrated composer in Europe. With the death of his patron Nikolaus Esterházy in 1790, Haydn was free to travel, and augmented his fame—now as a performer before the public—in both London and Vienna. The last years of his life (1803–1809) were spent in a state of debility, unable to compose due to poor health. He died in Vienna in 1809 at the age of 77.

Haydn was a friend and mentor of Mozart, a teacher of Beethoven, and the elder brother of composer Michael Haydn.