Underwater noise pollution poses a global threat to marine life and is a growing concern for policymakers and environmental managers. Underwater noise from human activities can impact individuals and populations of marine organisms in complex ways. Noise can reduce communication ranges and mask important animal sounds used for communication, but also for predator/prey detection. Evidence is mounting of noise‐induced habitat loss, excluding animals from important habitats, increase of physiological stress, disrupt reproductive and resting behaviours, and affect energy budgets by interfering with foraging. Noise can also cause temporary loss of hearing sensitivity and permanent loss of hearing ability, induce physical injury, and, in extreme cases, direct or indirect mortality. Initial studies focused on charismatic megafauna, such as cetaceans, but in recent years effects have been discovered in other taxa, from invertebrates to fish, and also diving seabirds. Unlike other marine pollutants such as microplastics or persistent organic contaminants, underwater noise is ephemeral and quickly disperses in the environment. If effective, interventions to reduce noise pollution could lead to a rapid easing of this pressure on acoustically sensitive organisms.