Sound travels fast in the sea and has good propagation abilities, which makes it an excellent mean of rapid information acquisition and exchange. Many marine animals have therefore developed auditory capabilities and rely on the sound to overcome the many challenges of living in the sea. However, the advantages of using sound (to communicate, locate prey, and navigate) have been jeopardized in recent times, as the world seas have become noisier. Noise generated by diverse human activities (anthropogenic noise) has altered the quality of the marine environment with consequences on physiology, communication, behavior, and energetics of different marine species. Their responses to sound depend on characteristics such as sound levels and frequency, duration of exposure to it, animals’ state and distance from the sound source, and they differ between species based on their hearing sensitivity. Anthropogenic sound in the sea is acknowledged as an important environmental stressor that can, in the long term, have detrimental consequences on the fitness, survival, and reproductive success of entire populations and species. Owing to this, the responsibility to minimize the environmental impact of noise on marine organisms has become a part of many international agreements and conventions. The effects of noise at the physiological and behavioral levels have been most studied in cetaceans and fish, though in more recent times, effects on invertebrates and larvae have also been identified. Here we summarize current knowledge on the sources of anthropogenic noise in the sea and the effects this humanly generated noise may have on different acoustically sensitive marine species.