For centuries, humans ignored sound in the “silent world” of the ocean, assuming that what we couldn’t perceive, didn’t exist. But we couldn’t have been more wrong. Marine scientists now have the technology to record and study the complex interplay of the myriad sounds in the sea. Finally, we can trace how sounds travel with the currents, bounce from the seafloor and surface, bend with the temperature and even saltiness; how sounds help marine life survive; and how human noise can transform entire marine ecosystems. In , award-winning science journalist Amorina Kingdon synthesizes historical discoveries with the latest scientific research in a clear and compelling portrait of this sonic undersea world. From plainfin midshipman fish, whose swim-bladder drumming is loud enough to keep houseboat-dwellers awake, to the syntax of whalesong; from the deafening crackle of snapping shrimp, to the seismic resonance of underwater earthquakes and volcanoes; sound plays a vital role in feeding, mating, parenting, navigating, and warning—even in animals that we never suspected of acoustic ability. Meanwhile, we jump in our motorboats and cruise ships, oblivious to the impact below us. Our lifestyle is fueled by oil in growling tankers and furnished by goods that travel in massive container ships. Our seas echo with human-made sound, but we are just learning of the repercussions of anthropogenic noise on the marine world’s delicate acoustic ecosystems—masking mating calls, chasing animals from their food, and even wounding creatures, from plankton to lobsters. With intimate and artful prose, tells a uniquely complete story of ocean animals’ submerged sounds, envisions a quieter future, and offers a profound new understanding of the world below the surface.