The Age of Reason; Being an Investigation of True and Fabulous Theology is an influential work . It follows in the tradition of eighteenth-century British deism, and challenges institutionalized religion and the legitimacy of the Bible (the central Christian text). It was a bestseller in America, where it caused a short-lived deistic revival. British audiences, however, fearing increased political radicalism as a result of the French Revolution, received it with more hostility.

The Age of Reason presents common deistic arguments; for example, it highlights what Paine perceives as corruption of the Christian Church and criticizes its efforts to acquire political power. Paine advocates reason in the place of revelation, leading him to reject miracles and to view the Bible as an ordinary piece of literature rather than as a divinely inspired text. It promotes natural religion and argues for a creator-God.

Thomas Paine was an English-American political activist, philosopher, political theorist and revolutionary. One of the Founding Fathers of the United States, he authored the two most influential pamphlets at the start of the American Revolution, and he inspired the rebels in 1776 to declare independence from Britain. His ideas reflected Enlightenment-era rhetoric of transnational human rights. He has been called "a corsetmaker by trade, a journalist by profession, and a propagandist by inclination".