The biggest whale is the female blue whale, which grows to be about 29 m long. The smallest whale is the dwarf sperm whale which as an adult is only 2.6 m long.

Whales are marine mammals and they breathe air into their lungs through blow-holes. Baleen whales, including the Blue Whale, the Humpback Whale and the Grey Whale, are larger than toothed whales. The Sperm Whale, Killer (Orca) Whale and the Beluga Whale are all examples of toothed whales.

Whales have a streamlined shape. Unlike many animals, whales have to stay conscious in order to breathe. When they sleep, only one side of their brains sleeps at a time. They are never completely asleep but still get the rest they need.