Gioachino Rossini, 1865

Gioachino Antonio Rossini (Italian pronunciation: [dʒoaˈkiːno anˈtɔːnjo rosˈsiːni] (Giovacchino Antonio Rossini in the baptismal certificate) (29 February 1792 – 13 November 1868) was an Italian composer who wrote 39 operas as well as sacred music, chamber music, songs, and some instrumental and piano pieces. His best-known operas include the Italian comedies Il barbiere di Siviglia (The Barber of Seville) and La Cenerentola and the French-language epics Moïse et Pharaon and Guillaume Tell (William Tell). A tendency for inspired, song-like melodies is evident throughout his scores, which led to the nickname "The Italian Mozart". Until his retirement in 1829, Rossini had been the most popular opera composer in history.

This list provides a guide to the most important opera composers, as determined by their presence on a majority of compiled lists of significant opera composers. (See the "Lists Consulted" section for full details.) The composers run from Jacopo Peri, who wrote the first ever opera in late 16th century Italy, to John Adams, one of the leading figures in the contemporary operatic world. The brief accompanying notes offer an explanation as to why each composer has been considered major. Also included is a section about major women opera composers, compiled from the same lists. For an introduction to operatic history, see Opera. The organisation of the list is by birthdate.