Józef Antoni Franciszek (sometimes Józef Ksawery Elsner, baptismal name Joseph Anton Franz Elsner; Grottkau, 1 June 1769 – 18 April 1854, Elsnerów, Elsner's estate, now within Warsaw) 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 (about 120 religious) works, and 38 operas. He is perhaps best known as teacher of the young Frédéric Chopin.

Joseph Elsner was born in Grottkau (Duchy of Nysa), near Breslau, Kingdom of Prussia, on June 1, 1769, to Silesian Catholic parents Franz Xaver Elsner. His mother was from the famous Matzke family of Glatz, which had intensive contacts with Czech culture in Bohemia. Joseph Elsner was educated at Breslau's Dominican monastery school, St. Matthew's Gymnasium, and a local Jesuit college. In 1832 – 37 he would compose nineteen religious pieces for Breslau Cathedral.

After completing his studies at Breslau and being a violinist at Brünn, in 1792 he became 2nd Kapellmeister at the German Opera in Austrian-ruled Lemberg. There in 1796 he married Klara Abt, who died a year later. In 1799, with Wojciech Bogusławski, he went to New East Prussia (Prussian-ruled Poland) and became the principal conductor, first at the German Theatre, then at the Polish National Theatre in Warsaw.

Elsner traveled to Paris, Dresden and Poznań, where he met E.T.A. Hoffmann. In 1802 he married a second wife, Karolina Drozdowska. Due to complaints that he preferred Germans, he resigned from Theater work.

During his decades in Warsaw, Elsner's name and family life gradually polonized. Elsner's ethnicity should not be evaluated in terms of 19th- and 20th-century national identity, as he probably considered himself primarily a Silesian.

Elsner taught the composers Ignacy Feliks Dobrzyński and Frédéric Chopin. Chopin dedicated to Elsner his celebrated Variations on "La ci darem la mano" from Mozart's Opera "Don Giovanni", Op. 2 (1827) and his Piano Sonata No. 1 in C minor, Op. 4 (1828) — both composed while Chopin was studying with Elsner.

In 1799 - 1824 Elsner was the principal conductor at Warsaw's National Theater, where he premiered a number of his operas. Elsner also taught at the Warsaw Lyceum, housed in the Kazimierz Palace.

In 1823 – 29 Elsner taught Chopin music theory and composition. At the time, Elsner wrote of Chopin in his diary: "Chopin, Frederic, third-year student, amazing capabilities, musical genius."

Elsner died at his estate in Elsnerów, now within the city limits of Warsaw, on April 18, 1854.