The main theme is called the melody. It consists of one or more musical phrases, and is usually repeated throughout a song or piece in various forms. Different musical styles use melody in different ways. For example:

• Rock music and other forms of popular music and folk music tend to pick one or two melodies (verse and chorus) and stick with them; much variety may occur in the phrasing and lyrics.

• In western classical music, composers often introduce an initial melody, or theme, and then create variations. Classical music often has several melodic layers, called polyphony, such as those in a fugue, a type of counterpoint. Often melodies are constructed from motifs or short melodic fragments, such as the opening of Beethoven's Ninth. Richard Wagner popularized the concept of a leitmotif: a motif or melody associated with a certain idea, person or place.

• Jazz musicians use the melody line, called the "lead" or "head", as a starting point for improvisation.

• Indian classical music relies heavily on melody and rhythm, and not so much on harmony as the above forms.

• Balinese gamelan music often uses complicated variations and alterations of a single melody played simultaneously, called heterophony.