Macau or Macao (Chinese: 澳門; Portuguese: Macau), officially the Macao Special Administrative Region of the People's Republic of China, is an autonomous territory on the western side of the Pearl River estuary in East Asia. Along with Hong Kong, Guangzhou, Shenzhen, Zhuhai, and several other major cities in Guangdong, the territory forms a core part of the Pearl River Delta metropolitan region, the most populated area in the world. With a population of 650,900 in an area of 30.5 km2, it is the most densely populated region in the world.
Macau was formerly a colony of the Portuguese Empire, after Ming China leased the territory as a trading post in 1557. Originally governing under Chinese authority and sovereignty, Portugal was given perpetual occupation rights for Macau in 1887. Macau remained under Portuguese control until 1999, when it was returned to China. As a special administrative region, Macau maintains a separate political and economic system apart from mainland China. The People's Republic of China's obligation to run Macau as a special administrative region per the Joint Declaration on the Question of Macau expires on 20 December 2049.
Macau is the gambling capital of the world. Its economy is heavily dependent on gambling and tourism, with the largest gambling revenue since 2006. It has a very high Human Development Index and the fourth-highest life expectancy in the world. Macau is among the world's richest regions and its GDP per capita by purchasing power parity was higher than that of any country in the world.