Why are expression markings often written in Italian?

In the context of musical notation, Italian became the dominant language for expression markings primarily because it established an international vocabulary that is taught to musicians alongside the fundamental principles of notation.1

During the 17th century, composers began introducing Italian terms to provide more methodical indications for tempo, such as adagio and allegro, which helped standardize performance styles. Similarly, the Venetian composer Giovanni Gabrieli introduced Italian terms like piano and forte to define dynamics, creating a system that remains in use today.1

While some composers in the 20th century began using their own native languages for these instructions, Italian persists as the standard international medium. This consistency ensures that performers from diverse backgrounds can interpret a score accurately, regardless of the composer's nationality.1