A repertoire is the songs a singer knows well and can perform. A singer's repertoire will be determined in part by his or her voice type. If a published song is in a key not suited to an individual, it's possible to transcribe it into a more suitable key. Often repertoire is published in several editions – in different keys for high or low voice, for example. In opera, repertoire may also refer to the characters a singer knows well; for example, a soprano may have as part of her repertoire: Susanna in The Marriage of Figaro, Adele in Die Fledermaus, and Olympia in The Tales of Hoffman.