In the western Pearl River Delta near the South China Sea, Macau, or Macao, officially known as the Macao Special Administrative Region of the People's Republic of China (MSAR),[e] is a city and special administrative region of China. It is the world's most populous region, covering 32.9 km2 (12.7 sq mi) and home to approximately 680,000 people.

The territory of Portuguese Macau was once a Portuguese colony. In 1557, the Ming dynasty leased it to Portugal for use as a trading post. The territory was administered by Portugal at a yearly rent and was under Chinese control until 1887. The Sino-Portuguese Treaty of Peking gave Portugal rights to be a colony forever. The colony was transferred to China in 1999, after which it remained under Portuguese control. Under the adage "one country, two systems," Macau is a special administrative region of China that operates independently of mainland China's governing and economic systems. In 2005, the city's historic center was included on the UNESCO World Heritage List due to its distinctive combination of Portuguese and Chinese architecture.
Macau, once a sparsely populated collection of coastal islands, is now a major resort city and a top gambling tourism destination, with a gambling industry seven times larger than Las Vegas'. In 2021, the city's GDP per capita by purchasing power parity is one of the highest in the world, with a per capita income of US$43,770. According to the Macau government's calculations, it has the fourth-highest life expectancy in the world and a very high Human Development Index. The area is heavily populated; Two-thirds of the land area is constructed on sea-reclaimed land.