Film music is extremely important in developing the atmosphere of scenes, accompanying scene changes, adding to the dramatic impact, and providing continuity across edits. The background music in a film is often referred to as underscoring. It adds to the mood of the scene, reinforcing dramatic developments and aspects of character.

When the music is precisely synchronised with events on screen this is known as Mickey-Mousing (e.g. someone falling could use a descending scale followed by a cymbal crash), this is common in comedy films.

Horror films often use atonal music, this music is not related to a tonic note and has no sense of key.

Film music composers often use motifs to help build a sense of continuity. A motif is a recurring musical idea which is associated with a particular character or place. These can be manipulated to fit what's happening in the film.