Sound is made of the most ephemeral stuff on Earth, insubstantial tremors of air. Yet sound is also the great connector and revealer. Because sound waves pass through and around obstacles, they link living beings into sonic information networks. Some of these networks are communicative — songs, music, and speech — and some amount to eavesdropping — predators and competitors listening to one another as they breathe, move, and eat. Listening, then, can reveal the unseen dynamics of the living world. In a time of crisis and rapid change, listening offers us a powerful way to connect and understand.