The conservation status of the toothed whales has worsened dramatically since 2001. Since then, more species have been listed in the IUCN Red List as Vulnerable and Nearly Threatened, while the Baiji river dolphin, which used to live in the Yangtze River, is now probably extinct. One major threat to toothed whales world wide is entanglement in fishing gear. This alone claimed an unsustainably high death toll and for 86% of all toothed whale species, entanglement and death in gillnets, traps, weirs, purse seines, longlines and trawls poses a major risk. Lack of food and forced dietary shifts due to overfishing pose additional threats to 13 species. This encyclopedia outlines the most recent findings in many areas of cetacean biology, from genetic work to habitat and dietary preferences, schooling and reactions to human induced noise. It will greatly facilitate the development and implementation of action plans that may help reduce the threats to many whale species. This ref