An anthropogenic cacophonySound travels faster and farther in water than in air. Over evolutionary time, many marine organisms have come to rely on sound production, transmission, and reception for key aspects of their lives. These important behaviors are threatened by an increasing cacophony in the marine environment as human-produced sounds have become louder and more prevalent. Duarteet al.review the importance of biologically produced sounds and the ways in which anthropogenically produced sounds are affecting the marine soundscape.Science, this issue p.eaba4658