English National Opera (ENO) is an opera company based in London, resident at the London Coliseum in St Martin's Lane. It is one of the two principal opera companies in London, along with The Royal Opera, Covent Garden. ENO's productions are sung in English.

The company's origins were in the late 19th century, when the philanthropist Emma Cons, later assisted by her niece Lilian Baylis, presented theatrical and operatic performances at the Old Vic, for the benefit of local people. Baylis subsequently built up both the opera and the theatre companies, and later added a ballet company; these evolved into ENO, the Royal National Theatre and The Royal Ballet, respectively.

Baylis acquired and rebuilt the Sadler's Wells theatre in north London, a larger house, better suited to opera than the Old Vic. The opera company grew there into a permanent ensemble in the 1930s. During the Second World War, the theatre was closed and the company toured British towns and cities. After the war, the company returned to its home, but it continued to expand and improve. By the 1960s, a larger theatre was needed. In 1968, the company moved to the London Coliseum and adopted its present name in 1974.

Among the conductors associated with the company have been Colin Davis, Reginald Goodall, Charles Mackerras, Mark Elder and Edward Gardner. The current music director of ENO is Martyn Brabbins. Noted directors who have staged productions at ENO have included David Pountney, Jonathan Miller, Nicholas Hytner, Phyllida Lloyd and Calixto Bieito. ENO's current artistic director is Daniel Kramer. In addition to the core operatic repertoire, the company has presented a wide range of works, from early operas by Monteverdi to new commissions, operetta and Broadway shows.

The company has aimed to present the standard operatic repertoire, sung in English, and has staged all the major operas of Mozart, Wagner and Puccini, and a wide range of Verdi's operas. Under Mackerras and his successors the Czech repertoire has featured strongly, and a broad range of French and Russian operas has been presented. The company has for decades laid stress on opera as drama, and has avoided operas where vocal display takes precedence over musical and dramatic content. In addition to the operatic staples, ENO has a history of presenting new works, and latterly of commissioning them.

In 1966, under the company's head of design, Margaret Harris, Sadler's Wells Theatre Design Course was founded; it later became Motley Theatre Design Course. ENO Baylis, founded in 1985, is the education department of ENO; it aims to introduce new audiences to opera and "to deepen and enrich the experience of current audiences in an adventurous, creative and engaging manner."The programme offers training for students and young professionals, and also workshops, commissions, talks and debates.