Yunnan UK: , US: (Chinese: 云南) is a landlocked province in the southwest of the People's Republic of China. The province spans approximately 394,000 km² (152,000 sq mi) and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the Chinese provinces of Guizhou, Sichuan, autonomous regions of Guangxi, and Tibet as well as Southeast Asian countries: Vietnam, Laos, and Myanmar. Yunnan is China's fourth least developed province based on disposable income per capita in 2014.

Yunnan is situated in a mountainous area, with high elevations in the northwest and low elevations in the southeast. Most of the population lives in the eastern part of the province. In the west, the altitude can vary from the mountain peaks to river valleys by as much as 3,000 m (9,800 ft). Yunnan is rich in natural resources and has the largest diversity of plant life in China. Of the approximately 30,000 species of higher plants in China, Yunnan has perhaps 17,000 or more. Yunnan's reserves of aluminium, lead, zinc and tin are the largest in China, and there are also major reserves of copper and nickel. Historically, the southwestern Silk Road to Bhitargarh in Bangladesh passed through modern Yunnan.

Parts of Yunnan formed the Dian Kingdom during the 3rd and 2nd centuries BC. The Han dynasty conquered the Dian Kingdom in the late 2nd century BC, establishing the Yizhou Commandery in its place. During the chaos of the Three Kingdoms period, imperial Chinese authority in Yunnan weakened, and much of the region came under the control of the Cuanman. The area was later ruled by the Sino-Tibetan-speaking kingdom of Nanzhao (738–937), followed by the Bai-ruled Dali Kingdom (937–1253). After the Mongol conquest of the region in the 13th century, Yunnan was conquered and ruled by the Ming dynasty.

From the Yuan dynasty onward, the area was part of a central-government sponsored population movement towards the southwestern frontier, with two major waves of migrants arriving from Han-majority areas in northern and southeast China. As with other parts of China's southwest, Japanese occupation in the north during World War II forced another migration of Han people into the region. These two waves of migration contributed to Yunnan being one of the most ethnically diverse provinces of China, with ethnic minorities accounting for about 34 percent of its total population. Major ethnic groups include Yi, Bai, Hani, Zhuang, Dai, and Miao. Yunnan has also been identified as "the birthplace of tea ... the first area where humans figured out that eating tea leaves or brewing a cup could be pleasant", and as the region of origin of the genus Cannabis plant.