An MUS file, or a file ending with the extension .mus, is a file that is read and saved by the popular commercial music notation program Finale. The .mus was the extension used by Finale until the release of MakeMusic Finale 2014, at which time the program began to use the extension .musx.
The file itself contains information that is specific to the functionality and features of Finale. Generally, this data includes the title, orchestration, notes, articulation, dynamic markings and page layout of notated musical works. Additionally, if present, MIDI (music instrument digital interface) data is stored within the .mus file; this information may include performance details, including dynamics and other expressive nuances, if instrumental parts were recorded as opposed to being entered manually. As a proprietary format, .mus files can only be read and written by MakeMusic products such as Finale. Though Finale can read MIDI files and create related musical scores, MIDI files do not typically store notation details, which are primarily notes, their properties and synthesizer settings. Other formats such as MusicXML — which Finale supports through the Dolet 6 Plugin — can be used to transfer notation details between other notation software applications such as Sibelius. These files, which end in .xml, do not support all Finale functionality as of 2014.