Fux was a prolific composer of vocal and instrumental music. His works include 19 operas, of which Costanza e fortezza (1723) is notable; 29 partitas, including the Concentus musico-instrumentalis (1701); 10 oratorios; and about 80 masses, of which the Missa canonica, (1708), written in canon. His book Gradus ad Parnassum" (1725; Steps to Parnassus) attempted to systematize contrapuntal practices. It was long the standard textbook on counterpoint and was studied by Wolfgang A. Mozart, Joseph Haydn, and other 18th-century composers.