The serie M A R S (Music and Aristocracy in Rome in the Seventeenth and Eighteenth Centuries) is dedicated to the complex interplay between music production and reproduction and forms of aristocratic representation around the early modern Papal court. The concept of conversion as confessional and spiritual change obtains a critical place in the research of history and the arts in early modernity. In this study the first attempt is made to examine the relation between this multifaceted concept and music, within the specific context of Rome in the first half of the 17th century. In the aristocratic circles around the Pope – in the anti-Protestant climate intensified by the Thirty Years’ War – the concept of conversion became an instrument of Chiesa militante and the paradigm of Roman identity, self-perception and self-representation. This book focuses on conversion as a topos in music, which helped to shape the new dramatic musical genres to an astonishing extent. In this sense, the study is a significant contribution to a changed understanding of musical works, which are examined here in direct connection with the confessional, political, urban and perception-theory premises of the early modern period.