thumb|right|250px|The Teatro alla Scala in Milan, Italy. Founded in 1778, La Scala is one of the world's most famous opera houses.

Opera is an art form in which singers and musicians perform a dramatic work (called an opera) which combines a text (called a libretto) and a musical score. Opera is part of the Western classical music tradition. Opera incorporates many of the elements of spoken theatre, such as acting, scenery and costumes and sometimes includes dance. The performance is typically given in an opera house, accompanied by an orchestra or smaller musical ensemble.

Opera started in Italy at the end of the 16th century (with Jacopo Peri's lost Dafne, produced in Florence around 1597) and soon spread through the rest of Europe: Schütz in Germany, Lully in France, and Purcell in England all helped to establish their national traditions in the 17th century. However, in the 18th century, Italian opera continued to dominate most of Europe, except France, attracting foreign composers such as Handel. Opera seria was the most prestigious form of Italian opera, until Gluck reacted against its artificiality with his "reform" operas in the 1760s. Today the most renowned figure of late 18th century opera is Mozart, who began with opera seria but is most famous for his Italian comic operas, especially The Marriage of Figaro, Don Giovanni, and Così fan tutte, as well as The Magic Flute, a landmark in the German tradition.

The first third of the 19th century saw the highpoint of the bel canto style, with Rossini, Donizetti and Bellini all creating works that are still performed today. It also saw the advent of Grand Opera typified by the works of Meyerbeer. The mid to late 19th century is considered by some a golden age of opera, led by Wagner in Germany and Verdi in Italy. This 'golden age' developed through the verismo era in Italy and contemporary French opera through to Puccini and Strauss in the early 20th century. During the 19th century, parallel operatic traditions emerged in Central and Eastern Europe, particularly in Russia and Bohemia. The 20th century saw many experiments with modern styles, such as atonality and serialism (Schoenberg and Berg), Neo-Classicism (Stravinsky), and Minimalism (Philip Glass and John Adams). With the rise of recording technology, singers such as Enrico Caruso became known to audiences beyond the circle of opera fans. Operas were also performed on (and written for) radio and television.

Operatic terminology

The words of an opera are known as the libretto (literally "little book"). Some composers, notably Richard Wagner, have written their own libretti; others have worked in close collaboration with their librettists, e.g. Mozart with Lorenzo da Ponte. Traditional opera consists of two modes of singing: recitative, the plot-driving passages often sung in a non-melodic style characteristic of opera, and aria (an "air" or formal song) in which the characters express their emotions in a more structured melodic style. Duets, trios and other ensembles often occur, and choruses are used to comment on the action. In some forms of opera, such as Singspiel, opéra comique, operetta, and semi-opera, the recitative is mostly replaced by spoken dialogue. Melodic or semi-melodic passages occurring in the midst of, or instead of, recitative, are also referred to as arioso. During the Baroque and Classical periods, recitative could appear in two basic forms: secco (dry) recitative, accompanied only by "continuo", which was often no more than a harpsichord; or accompagnato (also known as "strumentato") in which the orchestra provided accompaniment. By the 19th century, accompagnato had gained the upper hand, the orchestra played a much bigger role, and Richard Wagner revolutionised opera by abolishing almost all distinction between aria and recitative in his quest for what he termed "endless melody". Subsequent composers have tended to follow Wagner's example, though some, such as Stravinsky in his The Rake's Progress have bucked the trend. The terminology of the various kinds of operatic voices is described in Section 3 below.