Though baleen whales include some of the largest animals on earth, they eat only tiny organisms. Instead of teeth, baleen whales have hundreds of plates of fringe (baleen) hanging down from the roof of their mouths. Made of keratin (fingernail material), the fringe serves as a strainer to capture plankton and other small prey. Baleen whales do not swim fast in pursuit of prey. Rather, they take large mouthfuls of seawater that gets filtered as it passes through the baleen. The size of the baleen plates varies, to as long as 4 meters (13 feet) in bowhead whales. Plate size, along with texture of the fringe, is an adaptation to the whale's diet. Long, fine fringe works for capturing tiny plankton, while wider fringe is used for larger prey, such as crustaceans. Baleen wears away during use, but continues to grow throughout a whale's life.

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.