Cambodia ( (listen); also Kampuchea ; Khmer: កម្ពុជា, UNGEGN: Kâmpŭchéa [kampuciə]), officially the Kingdom of Cambodia, is a country located in the southern portion of the Indochinese Peninsula in Southeast Asia, spanning an area of 181,035 square kilometres (69,898 square miles), bordered by Thailand to the northwest, Laos to the north, Vietnam to the east, and the Gulf of Thailand to the southwest. The capital and largest city is Phnom Penh.

The region now known as Cambodia has been inhabited since prehistoric times. 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, which flourished for over 600 years. The Indianised kingdom facilitated the spread of first Hinduism and then Buddhism to much of Southeast Asia and undertook many religious infrastructural projects throughout the region. Angkor Wat is the most famous of these structures and is designated as a World Heritage Site. In the fifteenth century, Cambodia experienced a decline of power, while its neighbors Vietnam and Thailand grew stronger. In 1863, Cambodia became a protectorate of France, and later was part of French Indochina.

After a period of Japanese occupation during the Second World War, Cambodia gained independence from France in 1953. Despite Cambodia's neutrality, the Vietnam War extended into the country in 1965 via the Ho Chi Minh and Sihanouk trails. A 1970 coup installed the US-aligned Khmer Republic, until being overthrown by the Khmer Rouge in 1975. The Khmer Rouge ruled the country and carried out the Cambodian genocide from 1975 until 1979, when they were ousted in the Cambodian–Vietnamese War. The Vietnamese-occupied People's Republic of Kampuchea became the de facto government, with attempts to rebuild the country after the genocide mired by limited international recognition and ongoing conflict.

Following the 1991 Paris Peace Accords which formally ended the war with Vietnam, Cambodia was governed briefly by a United Nations mission (1992–93). The UN withdrew after holding elections in which around 90 percent of the registered voters cast ballots. The 1997 coup d'état consolidated power under Prime Minister Hun Sen and the Cambodian People's Party (CPP), who remain in power. Although constitutionally a multi-party state, the CPP dominates the political system and dissolved its main opposition party in 2017, making Cambodia a de facto one-party state.

The United Nations designates Cambodia as a least developed country. Cambodia is a member of the United Nations, ASEAN, the RCEP, the East Asia Summit, the WTO, the Non-Aligned Movement and La Francophonie. While per capita income remains low compared to most neighboring countries, Cambodia has one of the fastest-growing economies in Asia. Agriculture remains the dominant economic sector, with strong growth in textiles, construction, garments, and tourism leading to increased foreign investment and international trade. Rich in biodiversity and seasonal tropical forests, Cambodia has a high rate of deforestation and is considered among the most vulnerable countries to climate change.