Musical soundtracks became very popular in the 1940s through 1960s, around the same time musicals became worldwide hits. Moviegoers flocked to see screen-based adaptations of popular stage plays, which were perceived to be more accessible than their Broadway counterparts. This trend seems to be resurging, with the success of such Hollywood musicals as Moulin Rouge and Chicago.

What's in a musical soundtrack? First, the title song. Most musicals have titles that are based on their main song. For example, the musical "The Sound of Music" is titled after the song of the same title. The same is true for "Jesus Christ Superstar," which also had a song with the same title.

A title song does not necessarily become a hit song, though. In the case of "Jesus Christ Superstar," it was a minor song entitled "I Don't Know How to Love Him" that hit the top charts.

Most musical soundtracks not only contain all the songs used in the film, but even the background or incidental music. Background music refers to the sounds used during dialogue and transition scenes. This music is, more often than not, a purely instrumental version of themes or songs that are sung by the characters in other parts of the movie. Background music is incidental, which means it is passive and runs unacknowledged by the characters.

Almost all of the feature-length animated cartoons produced by such labels as Disney are musicals (the same is not true for Pixar, though). Animated films work just like their real-actor counterparts, but their soundtracks have one distinguishing characteristic - their music is more novel, done in the same tradition as nonmusical film soundtracks.

Soundtracks of animated musicals oftentimes become very sellable. Some commercial hits are songs performed by Cline Dion for "Beauty and the Beast," and songs performed by Elton John for the "The Lion King."