How to convey the desired tempo is a problem that every composer had to face before the invention of the metronome. In Mozart’s time, the players could only rely on the information provided by the tempo marks, as well as the implications provided by articulation, drama, rhythm and even common sense. According to Nikolaus Harnoncourt’s observations as express in his book The Musical Dialogue: Thoughts on Monteverdi, Bach and Mozart, Mozart has his own tempo system, and uses his tempo marks in a characteristic way. By exploring the usage of tempo marks in Mozart’s operas The Marriage of Figaro and Don Giovanni, and linking these discoveries to his last three symphonies, this dissertation aims to uncover the meaning of Mozart’s tempo marks, and in this way to establish guidance for the performance of his music.