The first part of this paper presents a systematic application of a functionalist perspective to the study of emotional communication in music performance. This involves the integration of ideas and concepts from psychological research on emotion and nonverbal communication with Brunswik's (1956) probabilistic functionalism and a modified version of his lens model. It is argued that this approach may provide the necessary theoretical foundation by generating useful questions, hypotheses, and ways of evaluating data from performance analyses and listening experiments. The second part reports an experimental study in which professional guitar players were instructed to play a short piece of music so as to communicate four basic emotions to listeners. The resulting performances were analyzed regarding various cues, such as tempo, sound level, and articulation. It was found that (a) the expressive intentions of the performers affected all of the measured cues in the performances, (b) the cues had merely a probabilistic relation to the performers' intentions, and (c) the cues were intercorrelated. The performances were also validated in a listening experiment which showed that listeners were successful in decoding the intended expression, and that there were no differences in decoding accuracy between musically trained and untrained listeners.