Xiangkhouang (Lao: ຊຽງຂວາງ, meaning 'Horizontal City'), also spelled Siang Khuang, is a province of Laos on the Xiangkhoang Plateau, in the nation's northeast. The province has the distinction of being the most heavily bombed place on Earth.

Historically, the province was formerly the independent principality of Muang Phuan. Its later capital is Phonsavan. The population of the province as of the 2015 census was 244,684.

Xiangkhouang province covers an area of 15,880 square kilometres (6,130 sq mi) and is mountainous. Apart from floodplains, the largest area of level land in the country is on the province's Xiangkhoang Plateau. The plateau is characterized by rolling hills and grassland whose elevation averages 1,300 metres (4,300 ft). The country's highest peak, Phou Bia (2,820 metres (9,250 ft)), rises at the south side of the plateau. Nam Et-Phou Louey is a National Biodiversity Conservation Area (NBCA) in the province, covering an area of 5,959 km², and overlaps into Houaphanh and Luang Prabang provinces.

The province's Plain of Jars was designated as a UNESCO World Heritage Site in 2019.

The Tai Phuan or Phuan people are a Buddhist Tai-Lao ethnic group that migrated to Laos from southern China. According to the Pongsawadan Meuang Puan ("Muang Puan Chronicles"), they were the first people who migrated in the 13th century from China to settle this province, forming the independent principality of Muang Phuan on the Plain of Jars, with Xieng Khouang (contemporary Muang Khoun) as its capital. They established an overland trade in metals and forest products with India and China; the Xieng Khouang Plateau was the center of trade for an area of upland Southeast Asia, extending as far as Da Nang in Vietnam, Samrong Sen in Cambodia, the Khorat Plateau in northeast Thailand, and the North Cachar Hills of northeastern India.

In the 14th century, Muang Phuan was subsumed into the Lan Xang kingdom under King Fa Ngum. Siamese invasions in 1777–1779, 1834–1836, and 1875–1876 sought to resettle the Phuan population into regions under firm Siamese control.

In the 1890s, the province came under French colonial rule following the 1893 Franco-Siamese crisis. During the Second Indochina War of the 1960s and 1970s, the province was a battleground in the Laotian Civil War, fought between royalist forces and the communist Pathet Lao until 1975, when the Pathet Lao emerged victorious and seized power over all of Laos. Xiangkhouang was the Lao province most bombed by the United States Air Force in support of royalist forces led by Hmong general Vang Pao, who was born in the province. As a result of this extensive air campaign, Muong Khoun, the original capital of the province, was virtually razed to the ground, resulting in the capital being moved to Phonsavan. During the wars, most of the 16th–19th century temples were completely destroyed, with only Wat Phia Wat temple having partially survived.

Xiangkhouang province covers an area of 15,880 square kilometres (6,130 sq mi) and has a largely mountainous topography. The province borders Luang Prabang province to the northwest, Houaphanh province to the northeast, Vietnam to the east, Bolikhamsai province to the southeast, and Vientiane province to the southwest. The capital is Phonsavan. Xiangkhouang and Vientiane provinces are part of the Nam Ngum River watershed.