This book introduces to the reader the subject of musical ontology by presenting it through different philosophical theories on the subject. By comparing these existing positions (such as mainstream ontological views, empirical stances, meta-ontolological reflections etc.), the book is an attempt to find what can be called a "reflective equilibrium" between the often conflicting intuitions in the studies and debates on philosophy of music. A balance which is ultimately able to respect both musical practice and ontological consistency.