In this article, Michael Zuckert traces the development of the various thinkers and groups who are known as the “Radical Whigs.” United in their opposition to centralized and absolute government, the Radical Whigs opposed Charles II and the Stuart kings, and strove to prevent the Catholic James from becoming king. While some of the Whigs advocated legal methods for this prevention, others (such as Algernon Sidney) advocated violent action. But with the Whig ascendancy in the Glorious Revolution, many Radical Whigs became disillusioned with the contemporary Whig leadership. Cato’s Letters, an anti-absolutist newspaper series, typified this second-wave Radical Whig philosophy. Second-wave Radical Whigs held to a social contract theory, inspired by Locke, in which men enter into society in order to preserve and secure their natural rights. Moreover, Cato’s Letters attempted to draw out the concrete implications of this Lockean philosophy in the areas of religion, constitutionalism, and economy, always championing freedom and decrying absolutism in any form. Most Radical Whigs, such as Richard Price and Joseph Priestly, also supported the American and French Revolutions.