Guangdong (UK: , US: ), formerly romanized as Canton or Kwangtung, is a coastal province in South China on the north shore of the South China Sea. The capital of the province is Guangzhou. With a population of 126.01 million (as of 2020) across a total area of about 179,800 km² (69,400 sq mi), Guangdong is the most populous province of China and the 15th-largest by area as well as the second-most populous country subdivision in the world (after Uttar Pradesh in India). Its economy is larger than that of any other province in the nation and the fifth largest sub-national economy in the world with a GDP (nominal) of 1.95 trillion USD (12.4 trillion CNY) in 2021. The Pearl River Delta Economic Zone, a Chinese megalopolis, is a core for high technology, manufacturing and foreign trade. Located in this zone are two of the four top Chinese cities and the top two Chinese prefecture-level cities by GDP; Guangzhou, the capital of the province, and Shenzhen, the first special economic zone in the country. These two are among the most populous and important cities in China, and have now become two of the world's most populous megacities and leading financial centres in the Asia-Pacific region.

The province of Guangdong surpassed Henan and Shandong to become the most populous province in China in January 2005, registering 79.1 million permanent residents and 31 million migrants who lived in the province for at least six months of the year; the total population was 104,303,132 in the 2010 census, accounting for 7.79 percent of Mainland China's population. This makes it the most populous first-level administrative subdivision of any country outside of South Asia. Its population increase since the census has been modest, the province registering 108,500,000 people in 2015. The vast majority of the historical Guangdong Province is administered by the People's Republic of China (PRC). Pratas Island in the South China Sea is part of Cijin District, Kaohsiung, Taiwan (ROC); the island was previously part of Guangdong Province before the Chinese Civil War.

Guangdong has a diversified economy. It was known as the starting point of the Maritime Silk Road of ancient China. Since 1989, Guangdong has topped the total GDP rankings among all provincial-level divisions, with Jiangsu and Shandong second and third in rank. In 2020, Guangdong's GDP nominal was 11 trillion RMB (1.7 trillion USD), exceeding that of Canada (US$1.64 trillion) and South Korea (US$1.63 trillion), the world's 9th and 10th largest economy, respectively. Compared to a country, it would be the 9th-largest economy as of 2020 and the 11th most populous. The province contributes approximately 9% of the total economic output of mainland China and is home to the production facilities and offices of a wide-ranging set of Chinese and foreign corporations. Guangdong has benefited from its proximity to the financial hub of Hong Kong, which it borders to the south. Guangdong also hosts the largest import and export fair in China, the Canton Fair, hosted in the provincial capital of Guangzhou.

After the unification of Lingnan region in the Qin dynasty, the immigrants from the Central Plains moved in and formed the local culture with a unique style. With the outward movement of the Guangdong people, the Hakka and Cantonese languages, music, cuisine, opera and tea ceremony have been spread throughout the nation, Southeast Asia and other countries. Guangdong was also the birthplace of the father of modern China and the founder of the Republic of China, Sun Yat-sen where he later declared a military government in the Warlord Era. The two special administrative regions of Hong Kong and Macau fall within the scope of Guangdong cultural influence, and Guangdong culture still has profound influences on the Chinese in Singapore and Malaysia.

Guangdong is also one of the leading provinces in research and education in China. Guangdong hosts 160 institutions of higher education, ranking first in South Central China region and 2nd among all Chinese provinces/municipalities after Jiangsu. As of 2022, two major cities ranked in the top 30 cities in the world (Guangzhou 10th and Shenzhen 28th) by scientific research output, as tracked by the Nature Index.