In article the formation of the doctrine of the constituent power of the people in an Euro-Atlantic civilization area is tracked. It is reasoned that the doctrine of the social contract and the theory of people’s sovereignty performed function of a source of legitimacy of the government in concrete historical conditions of their emergence. It is noted that recognition of the people a uniform source of the government became the conventional formula of the constitutional construction in the 20th century. The constitution nature as act of the constituent power of the people, and legislative, executive and judicial — as the founded authorities reveals. The socio-political and legal essence of institutes of a constituent and the constitutional referendum as instruments of realization of the constituent power is investigated. In historical aspect institutional opportunities for despotic regeneration of the government owing to abuses of institutes of a constituent and a national referendum in cases of social and political immaturity of society are lit.