The Blue Whale is the largest animal on the planet, weighing as much as 200 tons (approximately 33 elephants). It has a heart the size of a small car.

They are also one of the loudest animals on Earth. Their calls reach 188 decibels, (while a jet reaches 140 decibels) and their low frequency whistle can be heard for hundreds of miles.

Blue Whales have long, slender mottled grayish-blue bodies and appear blue underwater. They are known to grow up to around 30 meters long and live for around 73 years. Female blue whales give birth every two to three years.

An anatomically modern blue whale fossil found in southern Italy was dated to around 1.5 million years ago.

They are filter feeders and their diet consists almost exclusively of krill. They are generally solitary or gather in small groups.

They were abundant in nearly all the Earth's oceans until the end of the 19th century and were hunted to the point of near extinction by whalers, until a ban in 1966. Over 29,000 blue whales were recorded as killed in one year. The global population was estimated to be only 5,000–15,000 mature whales in 2018. They are now threatened by ship strikes, entanglement in commercial fishing gear, human made ocean noise (e.g. sonar), oceanic acidification (which affects krill) and pollutants.

The Blue Whale is listed under the Environment Protection and Biodiversity Conservation Act, 1999 (EPBC Act) as endangered.