Cambodia, officially the Kingdom of Cambodia, is a country in Mainland Southeast Asia. It is bordered by Thailand to the northwest, Laos to the north, and Vietnam to the east, and has a coastline along the Gulf of Thailand in the southwest. It spans an area of 181,035 square kilometres (69,898 square miles), dominated by a low-lying plain and the confluence of the Mekong river and Tonlé Sap, Southeast Asia's largest lake. It is dominated by a tropical climate. Cambodia has a population of about 17 million people, the majority of which are ethnically Khmer. Its capital and most populous city is Phnom Penh, followed by Siem Reap and Battambang.

In 802 AD, Jayavarman II declared himself king, uniting the warring Khmer princes of Chenla under the name "Kambuja". This marked the beginning of the Khmer Empire. The Indianised kingdom facilitated the spread of first Hinduism and then Buddhism to Southeast Asia and undertook religious infrastructural projects throughout the region, the most famous of which is Angkor Wat. In the 15th century, it began a decline in power until, in 1863, Cambodia became a French protectorate. Following Japanese occupation during World War II, Cambodia declared independence from France in 1953. The Vietnam War embroiled the country in civil war during the 1960s, culminating in a 1970 coup which installed the US-aligned Khmer Republic and the takeover of the communist Khmer Rouge in 1975. The Khmer Rouge ruled the country and carried out the Cambodian genocide from 1975 until 1979, until they were ousted during the Cambodian–Vietnamese War. Peace was restored by the 1991 Paris Peace Accords and subsequent United Nations peacekeeping mission, establishing a new constitution, holding the 1993 general election, and ending long-term insurgencies. The 1997 coup d'état consolidated power under Prime Minister Hun Sen and the Cambodian People's Party (CPP).

Cambodia is a constitutional monarchy and multi-party state, although the CPP dominates the political system. The UN designates Cambodia a least developed country. Agriculture remains its dominant economic sector, with growth in textiles, construction, garments, and tourism leading to increased foreign investment and international trade. Corruption, human rights issues and deforestation have remained challenges in Cambodia's post-conflict development. The official and most widely spoken language is Khmer, and the most widely practiced religion is Buddhism. The country's culture and traditions are shaped by its Angkorean heritage and international influences over its history.

The Kingdom of Cambodia is the official English name of the country. The English Cambodia is an anglicisation of the French Cambodge, which in turn is the French transliteration of the Khmer កម្ពុជា (Kâmpŭchéa, pronounced [kampuciə]). Kâmpŭchéa is the shortened alternative to the country's official name in Khmer ព្រះរាជាណាចក្រកម្ពុជា (Preăh Réachéanachâkr Kâmpŭchéa, pronounced [preah riəciənaːcak kampuciə]. The Khmer endonym កម្ពុជា Kâmpŭchéa derives from the Sanskrit name कम्बोजदेश Kambojadeśa, composed of देश Deśa ("land of" or "country of") and कम्बोज (Kamboja), referring to the descendants of Kambu (a legendary Indian sage from the ancient Indian kingdom of Kamboja). The term Cambodia was already in use in Europe as early as 1524, since Antonio Pigafetta cites it in his work Relazione del primo viaggio intorno al mondo (1524–1525) as Camogia.

Scholar George Coedes refers to a 10th-century inscription of a Cambodian dynastic legend in which the hermit Kambu Swayambhuva and the celestial nymph Mera unite and establish the Cambodian Solar royal dynasty (Kambu-Mera), that begins with the Chenla ruler Srutavarman and his son Sreshthavarman. Coedes suggests that the Kambu Swayambhuva legend has its origins in southern India, as a version of the Kanchi Pallava dynasty creation myth.

There exists evidence for a Pleistocene human occupation of what later is Cambodia, which includes quartz and quartzite pebble tools found in terraces along the Mekong River, in Stung Treng and Kratié provinces, and in Kampot province. Some archaeological evidence shows communities of hunter-gatherers inhabited the region during the Holocene: the most ancient archaeological discovery site in Cambodia is considered to be the cave of Laang Spean, which belongs to the Hoabinhian period. Excavations in its lower layers produced a series of radiocarbon dates around 6000 BC. Upper layers in the same site gave evidence of transition to Neolithic, containing the earliest dated earthenware ceramics in Cambodia.

Archaeological records for the period between the Holocene and Iron Age remain equally limited. An event in prehistory was the penetration of the first rice farmers from the north, which began in the third millennium BC. Prehistoric evidence are the "circular earthworks" discovered in the red soils near Memot and in the adjacent region of Vietnam in the latter 1950s. Their function and age are still debated, and some of them possibly date from the second millennium BC. Other prehistoric sites of somewhat uncertain date are Samrong Sen (not far from the ancient capital of Oudong), where the first investigations began in 1875, and Phum Snay, in the northern province of Banteay Meanchey.

Iron was worked by about 500 BC, with supporting evidence coming from the Khorat Plateau, in what later is Thailand. In Cambodia, some Iron Age settlements were found beneath Baksei Chamkrong and other Angkorian temples while circular earthworks were discovered at the site of Lovea kilometres north-west of Angkor. Burials testify to improvement of food availability and trade, and the existence of a social structure and labour organisation. Kinds of glass beads recovered from sites, such as the Phum Snay site in the northwest and the Prohear site in the southeast, suggest that there were two main trading networks at the time. The two networks were separated by time and space, which indicate that there was a shift from one network to the other at about the 2nd–4th century AD, probably due to changes in socio-political powers.