Macau (; 澳門; 澳门; "Bay gate"), also spelled Macao, officially known as the Macao Special Administrative Region of the People's Republic of China, is a special administrative region on the southern coast of the People's Republic of China. Macau lies on the western side of the Pearl River Delta across from Hong Kong, which is about 64 kilometers to the east, and it is also bordered by Guangdong of Mainland China to the north and the South China Sea to the east and south. With an estimated population of around 636,200 living in an area of 30.3 km2 (11.6 sq mi), it is the most densely populated region in the world.
As Portuguese Macau, it was administered by the Portuguese Empire and its inheritor states from the mid-16th century until late 1999, when it was the last remaining European colony in Asia under Portugal. Portuguese traders first settled in Macau in the 1550s. In 1557, Macau was rented to Portugal from Ming China as a trading port. The Portuguese Empire administered the city under Chinese authority and sovereignty until 1887, when Macau became a colony. Sovereignty over Macau was transferred to China on 20 December 1999. The Joint Declaration on the Question of Macau and Macau Basic Law stipulate that Macau operate with a high degree of autonomy until at least 2049, fifty years after the transfer.