Results of numerous experiments conducted over the past 15 years by using behavioural as well as brain imaging methods have shown that musical expertise influences brain anatomy, brain functions and behaviour. The musician’ brain is thus considered as a very good model of brain plasticity. Moreover, many results have demonstrated that musical expertise not only impacts on music processing but also on several aspects of speech processing including lexical pitch, sentence intonation and the metric structure of words. Conversely, recent results indicated that linguistic expertise with tone or quantity languages such as Mandarin Chinese, Thai, Finnish and Japanese, influences the processing of harmonic tones and musical intervals. We discuss possible interpretations of these findings in terms of common processing of the acoustic parameters involved in music and speech and in terms of bidirectional transfer of training effects between music and speech processing.