Józef Antoni Franciszek Elsner (sometimes Józef Ksawery Elsner; baptismal name, Joseph Anton Franz Elsner) was a composer, music teacher, and music theoretician, active mainly in Warsaw. He was one of the first composers in Poland to weave elements of folk music into his works. He composed many symphonic, chamber, solo, and vocal-instrumental (some 120 of them, religious) works, and 38 operas. He is perhaps best known as the principal piano teacher of the young Frédéric Chopin.