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. While the scale of opera can be larger or smaller—there are many different genres of opera—performance typically involves different types of artist (singers, instrumentalists and often dancers and actors) and technical staff. Usually an orchestra led by a conductor accompanies the singers. In contrast to spoken theatre, the opera world is international. Italian, German, French, English, and Russian works are performed worldwide in their original languages, and artists travel from country to country performing.