Buddhism in Cambodia or Khmer Buddhism has existed since at least the 5th century. In its earliest form it was a type of Mahāyāna Buddhism. Today, the predominant form of Buddhism in Cambodia is Theravada Buddhism. It is enshrined in the Cambodian constitution as the official religion of the country. Theravada Buddhism has been the Cambodian state religion since the 13th century. As of 2019 it was estimated that 97. 1 percent of the population are Buddhists.

Maha Ghosananda was a highly revered Cambodian Buddhist monk in the Theravada tradition, who served as the Patriarch (Sangharaja) of Cambodian Buddhism during the Khmer Rouge period and post-communist transition period of Cambodian history. His Pali monastic name, 'Mahā Ghosānanda', means "great joyful proclaimer". He was well known in Cambodia for his annual peace marches.