Cambodia has a population of over 15 million. The official religion is Theravada Buddhism, practiced by approximately 95 percent of the population. The country's minority groups include Vietnamese, Chinese, Chams, and 30 hill tribes.^[7] The capital and largest city is Phnom Penh, the political, economic, and cultural centre of Cambodia. The kingdom is a constitutional monarchy with Norodom Sihamoni, a monarch chosen by the Royal Throne Council, as head of state. The head of government is Hun Sen, who is currently the longest serving non-royal leader in South East Asia and has ruled Cambodia for over 30 years.