For over 40 years, Andrew Barker has been studying the ways in which ancient Greek philosophers, scientists and others analysed and discussed the structures underlying musical compositions; he has focused, in particular, on their methodologies, the conceptual frameworks within which their analyses were formed, and the various philosophical commitments they brought to their work. This volume contains a selection of the essays that Barker has published on these and related topics. The essays are preceded by an English version of his book on 'psychomusicology', previously published only in Italian. It examines Greek writers' diverse and often influential speculations about correlations between musical structures and their counterparts in the soul, speculations which led them to striking conclusions about music's practical value in human affairs, and to recommendations for appropriate ways of employing it in such fields as - for example - moral education, psychotherapy, and the organization and governance of a healthy society.