This introductory chapter sets out the scope of Aural Diversity, with reference to acoustic environments and soundscape, music, and musicology. It challenges the tacit assumptions of normal hearing that underpin the majority of sound-related disciplines. It surveys existing literature in a range of sound-based disciplines. It describes the Aural Diversity project and summarises the various parts and chapters of this book. It proposes Aural Diversity as a paradigmatic shift, asking the question: whose ear has primacy?