Australia, officially known as the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. It is the largest country in Oceania and the world's sixth-largest country by total area. Australia is a parliamentary democracy and a constitutional monarchy with Queen Elizabeth II as the reigning monarch. The country is known for its unique wildlife, including kangaroos and koalas, as well as its iconic landmarks such as the Sydney Opera House and the Great Barrier Reef.