Khmer people (ខ្មែរ, English pronunciation: /ˈkmɛər/ or /kəˈmɛər/) are the predominant ethnic group in Cambodia, accounting for approximately 90% of the 14.8 million people in the country. They speak the Khmer language, which is part of the larger Mon–Khmer language family found throughout Southeast Asia. The majority of the Khmer are followers of the Khmer style of Buddhism, a highly syncretic version which blends elements of Theravada Buddhism, Hinduism, animism and ancestor-spirit worship. Significant populations of Khmers reside in adjacent areas of Thailand (Northern Khmer) and the Mekong Delta region of neighboring Vietnam (Khmer Krom).

Migrations into the mainland regions of Southeast Asia from the north continued well into historic times.^{[citation needed]} Most scholars believe they came at least 3,000 years ago, much earlier than Tai people who now inhabit many parts of what was originally Austroasiatic territory. The reason they migrated into Southeast Asia is generally debated, but scholars believe that Mon–Khmer were pushed down by invading Sino-Tibetans from the north as evident by Austroasiatic vocabulary in Chinese or because of agricultural purposes as evident by their migration routes along major rivers. The Khmer are relatives to the Mon who settled further to the west.