Nanjing (; Chinese: 南京; pinyin: Nánjīng, Mandarin pronunciation: [nǎn.tɕíŋ] (listen)), alternately romanized as Nanking, is the capital of Jiangsu province of the People's Republic of China. It is a sub-provincial city, a megacity, and the third largest city in Eastern China. The city has 11 districts, an administrative area of 6,600 km² (2,500 sq mi), and a total recorded population of 9,423,400 as of 2021.

Situated in the Yangtze River Delta region, Nanjing has a prominent place in Chinese history and culture, having served as the capital of various Chinese dynasties, kingdoms and republican governments dating from the 3rd century to 1949, and has thus long been a major center of culture, education, research, politics, economy, transport networks and tourism, being the home to one of the world's largest inland ports. The city is also one of the fifteen sub-provincial cities in the People's Republic of China's administrative structure, enjoying jurisdictional and economic autonomy only slightly less than that of a province. Nanjing has been ranked seventh in the evaluation of "Cities with Strongest Comprehensive Strength" issued by the National Statistics Bureau, and second in the evaluation of cities with most sustainable development potential in the Yangtze River Delta. It has also been awarded the title of 2008 Habitat Scroll of Honor of China, Special UN Habitat Scroll of Honor Award and National Civilized City. Nanjing is also considered a Beta (global second-tier) city classification, together with Chongqing, Hangzhou and Tianjin by the Globalization and World Cities Research Network, and ranked as one of the world's top 100 cities in the Global Financial Centres Index.

Nanjing has many highly ranked educational institutions, with the number of universities (13) listed in 147 Double First-Class Universities ranking third (after Beijing and Shanghai), including Nanjing University, which has a long history and is among the world's top 20 universities ranked by Nature Index. The ratio of college students to the total population ranks No.1 among large cities nationwide. Nanjing has the eighth-largest scientific research output of any city in the world. As of 2022, it has been regarded as the world's top second scientific research center in earth & environmental sciences after Beijing and the world's top third scientific research center in chemistry (behind Beijing and Shanghai), according to the Nature Index.

Nanjing, one of the nation's most important cities for over a thousand years, is recognized as one of the Four Great Ancient Capitals of China. It has been one of the world's largest cities, enjoying peace and prosperity despite wars and disasters. Nanjing served as the capital of Eastern Wu (229–280), one of the three major states in the Three Kingdoms period; the Eastern Jin and each of the Southern dynasties (Liu Song, Southern Qi, Liang and Chen), which successively ruled southern China from 317 to 589; the Southern Tang (937–75), one of the Ten Kingdoms; the Ming dynasty when, for the first time, all of China was ruled from the city (1368–1421); and the Republic of China under the nationalist Kuomintang (1927–37, 1946–49) before its flight to Taiwan by Chiang Kai-Shek during the Chinese Civil War. The city also served as the seat of the rebel Taiping Heavenly Kingdom (1853–64) and the Japanese puppet regime of Wang Jingwei (1940–45) during the Second Sino-Japanese War. It suffered severe atrocities in both conflicts, most notably the Nanjing massacre of 1937.

Nanjing has served as the capital city of Jiangsu province since the establishment of the People's Republic of China. It has many important heritage sites, including the Presidential Palace and Sun Yat-sen Mausoleum. Nanjing is famous for human historical landscapes, mountains and waters such as Fuzimiao, Ming Palace, Chaotian Palace, Porcelain Tower, Drum Tower, Stone City, City Wall, Qinhuai River, Xuanwu Lake and Purple Mountain. Key cultural facilities include Nanjing Library, Nanjing Museum and Jiangsu Art Museum.