Harmony is the simultaneous sounding of two or more notes in a way that is pleasant or desired. It is one of the main elements of Western music, along with melody, rhythm and timbre. It is often described as being concerned with the vertical aspect of music, as distinguished from the melodic line, which is the horizontal aspect.
Harmony differs from counterpoint, which deals with the relationship between simultaneous and coordinated melodic lines, and polyphony, which refers to the simultaneous sounding of independent melodies. The study of harmony includes chords and their construction as well as chord progressions and the principles of connection that govern them.