Xiamen, historically romanized as Amoy, is a sub-provincial city in southeastern Fujian, People's Republic of China, beside the Taiwan Strait. It is divided into six districts: Huli, Siming, Jimei, Tong'an, Haicang, and Xiang'an. All together, these cover an area of 1,700.61 square kilometers (656.61 sq mi) with a population of 5,163,970 as of 2020 and estimated at 5.35 million as of 31 December 2024. The urbanized area of the city has spread from its original island to include most parts of all six of its districts, as well as 4 Zhangzhou districts (Xiangcheng, Longwen, Longhai and Changtai), which form a built-up area of 7,284,148 inhabitants. This area also connects with Quanzhou in the north, making up a metropolis of nearly ten million people. The Kinmen Islands (Quemoy) administered by the Republic of China (Taiwan) lie less than 6 kilometers (4 mi) away separated by Xiamen Bay. As part of the Opening Up Policy under Deng Xiaoping, Xiamen became one of China's original four special economic zones opened to foreign investment and trade in the early 1980s.

Xiamen Island possessed a major international seaport. The port of Xiamen is a well-developed first-class trunk line port in the Asia-Pacific region. It is ranked the 7th-largest container port in China and ranks 14th in the world. It is the 4th port in China with the capacity to handle 6th-generation large container ships. On 31 August 2010, Xiamen Port incorporated the neighboring port of Zhangzhou to form the largest port of China's Southeast. Ever since the 12th century, Xiamen was also an important origin for many migrants to Singapore, Malaysia, Indonesia and the Philippines. The overseas Chinese used to support Xiamen's educational and cultural institutions. Xiamen is classified as a Large-Port Metropolis.

Xiamen is one of the top 40 cities in the world by scientific research as tracked by the Nature Index. The city is home to several major universities, including Xiamen University, one of China's most prestigious universities as a member of the Double First Class Universities, Huaqiao, Jimei, Xiamen University of Technology and Xiamen Medical College.

Xiamen had always been known as Tong'an County since antiquity until Republic of China Era of the 20th century, followed by administrative zoning restructures and naming changes.

Tong'an County first appeared in Han dynasty records. Xiamen Island was described as Jiahe Islet of Tong'an County during the Song dynasty (960–1279). It received its present name from the Xiamen Defense Castle erected on the island by Zhou Dexing in 1387 during the Ming dynasty to meet the needs of coastal defense. The name was formerly written using, Chinese: 下門; lit. 'Lower Gate', and then changed into Chinese: 廈門; lit. 'Mansion Gate' or "Gate of China".

After the fall of the Ming dynasty, Zheng Chenggong, or Koxinga, a Ming loyalist and general, occupied Xiamen island as an anti-Qing base. In 1650, the seventh year of Emperor Shunzhi of the Qing dynasty, Zheng set a military base in Xiamen island and changed its name into Chinese: 思明州; pinyin: Sīmíng zhōu; Pe̍h-ōe-jī: Su-bêng chiu; lit. 'Think Ming (dynasty) Prefecture', meaning "Remembering the Ming".

When its port prospered under the Qing, especially during the reign of Emperor Kangxi, the island's name was changed to Chinese: 廈門; pinyin: Xiàmén; Pe̍h-ōe-jī: Ē-mn̂g / Ē͘-mûi again.

The island's name of 思明 was in return restored after the Xinhai Revolution that inaugurated the republic in 1912.^{[citation needed]}