This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book describes the symmetrical opposition between musical mediation, understood as a model for the collective construction of an object, and its mirror image. It emphasises the importance of using mediation as a guide through the social sciences, works of art and music. The book reviews the Durkheimian model of belief. From a variety of angles, social interpretations of art have attempted to restore all the different sorts of mediators – human, institutional, material – which channel its relationship with its public. The book focuses on the reinterpretations of Baroque music, which looked at these interpretations in the light of a theory of mediation. It presents a series of case studies and ethnographical analyses, covering the various aspects of musical reality, from instruments to teaching techniques, from performance to recording.