Jiangsu is a coastal province in East China. It is one of the leading provinces in finance, education, technology, and tourism, with its capital in Nanjing. Jiangsu is the third smallest, but the fourth most populous, with a population of 84.75 million, and the most densely populated of the 22 provinces of the People's Republic of China. Jiangsu has the highest GDP per capita and second-highest GDP of Chinese provinces, after Guangdong. Jiangsu borders Shandong in the north, Anhui to the west, and Zhejiang and Shanghai to the south. Jiangsu has a coastline of over 1,000 kilometers (620 mi) along the Yellow Sea, and the Yangtze flows through the southern part of the province.

Since the Sui and Tang dynasties, Jiangsu has been a national economic and commercial center, partly due to the construction of the Grand Canal. Cities such as Nanjing, Suzhou, Wuxi, Changzhou, and Shanghai (separated from Jiangsu in 1927) are all major Chinese economic hubs. Since the initiation of economic reforms in 1990, Jiangsu has become a focal point for economic development. It is widely regarded as one of China's most developed provinces, when measured by its Human Development Index (HDI). Its 2021 nominal GDP per capita reached CN¥137,300 (US$21,287), becoming the first province in China to reach the $20,000 mark.

Jiangsu is home to many of the world's leading exporters of electronic equipment, chemicals and textiles. It has also been China's largest recipient of foreign direct investment since 2006. In 2022, its GDP was more than CN¥12.29 trillion (US$1.83 trillion nominal), which is the sixth-highest of all administrative divisions. If it were a country, it would be the twelfth-largest economy as of 2022 as well as the 19th most populous.

Jiangsu is also one of the leading provinces in research and education in China. As of 2022^[update], Jiangsu hosts 168 institutions of higher education, ranking first of all Chinese provinces. Jiangsu has many highly ranked educational institutions, with 16 number of universities listed in the Double First-Class Construction, ranking second after Beijing. As of 2023, four major cities in Jiangsu ranked in the world's top 200 (Nanjing 6th, Suzhou 40th, Zhenjiang 166th and Wuxi 188th) cities by scientific research output, as tracked by the Nature Index.

Jiangsu's name is a compound of the first elements of the names of the two cities of Jiangning (now Nanjing) and Suzhou. The abbreviation for this province is "苏" (Sū), the second character of its name.

During the earliest Chinese dynasties, the area that is now Jiangsu was far away from the center of Chinese civilization, which was in the northwest Henan; it was home of the Huai barbarians (淮夷), an ancient ethnic group. During the Zhou dynasty more contact was made, and eventually the state of Wu appeared in southern Jiangsu, one of the many hundreds of states that existed across northern and central China at that time. Near the end of the Spring and Autumn period, Wu became a great power under King Helu of Wu, and defeated in 484 BC the state of Qi, a major power in the north in modern-day Shandong province, and contest for the position of overlord over all states of China. The state of Wu was subjugated in 473 BC by the state of Yue, another state that had emerged to the south in modern-day Zhejiang province. Yue was in turn subjugated by the powerful state of Chu from the west in 333 BC. Eventually the state of Qin swept away all the other states, and unified China in 221 BC.

Under the reign of the Han dynasty (206 BC to 220 AD), Jiangsu was removed from the centers of civilization in the North China Plain, and was administered under two zhou (provinces): Xu Province in the north, and Yang Province in the south. During the Three Kingdoms period, southern Jiangsu became the base of the Eastern Wu (222 to 280), whose capital, Jianye (later renamed to Jiankang), is modern Nanjing. When nomadic invasions overran northern China in the 4th century, the imperial court of the Jin dynasty moved to Jiankang. Cities in southern and central Jiangsu swelled with the influx of migrants from the north. Jiankang remained as the capital for four successive Southern dynasties and became the largest commercial and cultural center in China.

After the Sui dynasty united the country in 581, the political center of the country shifted back to the north, but the Grand Canal was built through Jiangsu to link the Central Plains with the prosperous Yangtze Delta. The Tang dynasty (618–907) relied on southern Jiangsu for annual deliveries of grain. It was during the Song dynasty (960–1279), which saw the development of a wealthy mercantile class and emergent market economy in China, that Jiangnan (southern Jiangsu, Shanghai, and adjacent areas) emerged as a center of trade. From then onwards, major cities like Suzhou or Yangzhou, would be synonymous with opulence and luxury in China. Today the region remains one of the richest parts of China.