Musica universalis or music of the spheres is a medieval philosophical concept that regards the proportions in the movements of the celestial bodies - the sun, moon and planets - as a form of musica (the medieval Latin name for music). This music was not thought of as an audible sound, but simply as a mathematical concept. The Greek philosopher Pythagoras was frequently credited with originating the concept, which stemmed from his semi-mystical, semi-mathematical philosophy and its associated system of numerology. (See pythagoreanism.)

At the time, the sun, moon and planets were thought to revolve around the earth in their proper spheres - the most thorough and imaginative description of the concept can be found in Dante's Divine Comedy. The spheres were thought to have been created by God in proportional relations that were reflected in the whole-number relations of the pure musical intervals.

The medieval concept of music comprised three different forms of musica: musica universalis, musica mundana, and musica instrumentalis. Only musica instrumentalis actually referred to sounds made by musicians (both singers and instrumentalists).