This book presents the first book-length study of ambient sound as a key issue in sound studies and sonic philosophy. Taking a broad, media-philosophical approach, it explores ambient sound as a basic dimension of the sonic environment, sonic technologies, sonic arts and the material staging of listening. Through analyses of key concepts such as surroundability, mediatization, immanence, synthetization and continuous variation, the book elucidates how ambient aspects of sound influence our conceptions of what sound is and how it affects us by exposing sound’s relation to basic categories such as space, time, environment, medium and materiality. It also illuminates how the strategic production of ambient sound constitutes a leading aesthetic paradigm that has been a decisive factor in the shaping of the modern sonic environment – from key developments in experimental and popular music, sound art and cinematic sound design to the architectural-technological construction of listening spaces in concert halls and theaters and in current streaming infrastructures, digital surround sound and the everyday aesthetics of headphone listening.