Humans have hunted baleen whales since prehistoric time. Archaeological remains from several thousand years ago show evidence of whaling in Norse and Alaskan Eskimo settlements. Large-scale commercial whaling reached its peak beginning in the 18th century, with Scandinavians, Dutch, British, Japanese, and later the former Soviet Union taking part. Because whales have few young over long periods of time, their populations do not recover quickly from loss. By the late 1700s, some whale populations were already collapsing from overhunting. New technologies, such as steam ships and explosive harpoon guns, reduced whale numbers even more, and the discovery of Arctic feeding grounds for whales in the early 1900s created a new opportunity for hunters. Commercial whaling was banned in 1986, and some populations began a slow recovery. Other populations remain threatened by continued whaling by some countries, incidental capture in fishing operations, and human impacts such as pollution, noise, and global climate change.

All cetaceans are aquatic, and they swim by pumping their tail up and down, using paddle-like flippers for steering. The tail fins (flukes) are flexible, with no bones, and attached to the body with cartilage. Huge back muscles power the tail, making them powerful swimmers. Cetaceans are also good divers, some able to stay underwater for hours and reach depths of hundreds of meters. As air breathers, they must hold their breath to dive, yet their lungs are small and compress to an even smaller size during a dive. The stored air is pushed into their windpipe, where a thickened lining keeps it out of contact with the rest of the body. Sealing off the air prevents a buildup of nitrogen (from air) in the bloodstream, which protects cetaceans from the "bends" that human divers are in danger of when they submerge. During diving, oxygen reserves stored in special molecules (myoglobin) supply oxygen to cetaceans' bodies.