The Age of Reason; Being an Investigation of True and Fabulous Theology is a book written by English and American political activist Thomas Paine. It defends the philosophical position of deism. It follows in the tradition of 18th-century British deism, and challenges the official religion and the authority of the Bible. It was published in three parts in 1794, 1795, and 1807.
It was a best-seller in the United States, where it was the cause for a coming back of deism. However, it was not well received in Britain, because the public feared increased political radicalism as a result of the French Revolution.
The Age of Reason presents common deistic arguments; for example, it highlights what Paine saw as corruption of the Christian Church. Paine preferes reason in the place of revelation, leading him to reject miracles and to view the Bible as an ordinary book, rather than a text given by God. In The Age of Reason, he promotes natural religion and argues for the existence of a creator god.