In this article, Walter Berns outlines the history of ideas leading up to the modern constitutional principles embodied in the Constitution of the United States. The most salient principle in modern constitutionalism is that of popular sovereignty: the belief that a government derives its legitimacy from the consent of those governed. This principle, which can be traced to John Locke, marked a significant break from the British constitutional system, whose authority extended from a long-standing heritage of contract, precedent, and common law. Though the American Founders relied on many British ideas in the formulation of their Constitution, they justified the American Revolution, not on the basis of tradition or their rights as Englishmen, but by appealing to the universal natural rights to which all men are entitled. The other key principle of modern constitutionalism explored in the article is that of limited government, achieved by means of a written constitution that moderates majority rule by complex representative arrangements and institutional contrivances.