This study investigates the role of expertise in the listener judgment of emotion in music. Previous studies suggest that the most important factors are mode and tempo, respectively influencing valence and arousal. The effect is stronger when the two parameters converge (major mode combined with fast tempo and vice versa), whereas tempo predominates when they do not converge. An open question is whether and how these judgments vary with the expertise of the listener. Our hypothesis is that non-experts will base their evaluation mainly on tempo, disregarding mode, which is more complex to be aware of. On the other hand, experts will take advantage of both sources of information. The experiment involved 40 participants. Experts were stu-dents who attended at least five years at music school. Non-experts had no formal musical training. Valence (positive vs. negative) and arousal (high vs. low) were manipulated independently in a 2*2 within-subjects de-sign. Seven short piano pieces were composed and manipulated using the four conditions, for a total of 28 snippets. For each snippet, participants were asked to rate the values of the experienced valence and arousal on a seven-point scale. Results confirmed that for both types of listeners arousal was determined exclusively by tempo. Valence was primarily influenced by mode. Non-experts were also influenced by tempo for valence evaluation, while experts were not. As regards valence, mode is predominant in cases of divergent conditions but only for experts. Implications of these findings for the design of computing systems to allow non-musicians to create music are discussed.