Shanghai is the largest city in China, and one of the largest metropolitan areas in the world, with over 20 million people.  Located on China's central eastern coast just at the mouth of the Yangtze River, the city is administered as a municipality of  the People's Republic of China with province-level status. Originally a fishing and textiles town, Shanghai grew to importance in the 19th century due to its favorable port location and as one of the cities opened to foreign trade by the 1842 Treaty of  Nanking. The city flourished as a center of commerce between east and west, and became a multinational hub of finance and business by the 1930s. Shanghai's prosperity was interrupted after the 1949 Communist takeover and the subsequent  cessation of foreign investment. After 1990, the economic reforms introduced by Deng Xiaoping resulted in intense re-development and financing in Shanghai, and in 2005 Shanghai became the world's largest cargo port.

The city is a tourist destination renowned for its historical landmarks such as the Bund and City God Temple, its modern and ever-expanding Pudong skyline including the Oriental Pearl Tower, and its new reputation as a cosmopolitan center of culture and design. Today, Shanghai is the largest center of commerce and finance in mainland China, and has been described as the "showpiece" of the world's fastest-growing major economy.

The urban area of Shanghai can be seen in this false-color satellite image.Shanghai sits on the Yangtze River Delta on China's eastern coast, and is roughly equidistant from Beijing and Hong Kong. The municipality as a whole consists of a peninsula  between the Yangtze and Hangzhou Bay, China's third largest island Chongming, and a number of smaller islands. It is bordered on the north and west by Jiangsu Province, on the south by Zhejiang Province, and on the east by the East China Sea. The city proper is bisected by the Huangpu River, a tributary of the Yangtze. The historic center of the city, the Puxi area, is located on the western side of the Huangpu, while a new financial district, Pudong, has developed on the eastern bank.

The vast majority of Shanghai's 6,218 km2 (2,401 sq mi) land area is flat, apart from a few hills in the southwest corner, with an average elevation of 4 m (13 ft). The city's location on the flat alluvial plain has meant that new skyscrapers must be built with deep concrete piles to stop them sinking into the soft ground. The highest point is at the peak of Dajinshan Island at 103 m (340 ft). The city has many rivers, canals, streams and lakes and is known for its rich water resources as part of the Taihu drainage area.

A park in the center of ShanghaiPublic awareness of the environment is growing, and the city is investing in a number of environmental protection projects. A 10-year, US$1 billion cleanup of Suzhou Creek, which runs through the city center, is expected to be finished in 2008, and the government also provides incentives for transportation companies to invest in LPG buses and taxis. Air pollution in Shanghai is low compared to other Chinese cities such as Beijing, but the rapid development over the past decades means it is still high on worldwide standards, comparable to Los Angeles.

Shanghai has a humid subtropical climate (Koppen climate classification Cfa) and experiences four distinct seasons. In winter,  cold northerly winds from Siberia can cause nighttime temperatures to drop below freezing, although most years there are only one or two days of snowfall. Summer in Shanghai is very warm and humid, with occasional downpours or freak thunderstorms. The city is also susceptible to typhoons, none of which in recent years has caused considerable damage. The most pleasant seasons are Spring, although changeable, and Autumn, which is generally sunny and dry. Shanghai experiences on average 1,878 hours of sunshine per year, with the hottest temperature ever recorded at 40 °C (104 °F), and the lowest at -12 °C (10 °F). The average number of rainy days is 112 per year, with the wettest month being June. The average frost-free period is 276 days.