The research presented in this paper is focused on global tempo transformations of music performances. We are investigating the problem of how a performance played at a particular tempo can be rendered automatically at another tempo, while preserving naturally sounding expressivity. Or, differently stated, how does expressiveness change with global tempo. Changing the tempo of a given melody is a problem that cannot be reduced to just applying a uniform transformation to all the notes of a musical piece. The expressive resources for emphasizing the musical structure of the melody and the affective content differ depending on the performance tempo. We present a case-based reasoning system called TempoExpress and will describe the experimental results obtained with our approach.This research has been partially supported by the Spanish Ministry of Science and Technology under the project TIC2003-07776-C2-02 "CBR-ProMusic" and EU-FEDER fundsPeer reviewed