Denis Diderot, an important figure in the 18th-century French Encyclopedist movement, believed in the Enlightenment ideals of rationality and human progress, according to the Internet Encyclopedia of Philosophy; these beliefs are apparent in his work on the Encyclopedie. Diderot was also a political radical, and he openly expressed atheism in many of his essays and other literary work.
Diderot was the general editor of the Encyclopedie, a massive effort to disseminate knowledge, especially of technology and the mechanical arts, to the general population. The contributors to this project believed that this knowledge could overcome the reactionary and religious sentiments of the era. Enlightenment philosophers thought that reason and intellect should guide society and that the scientific method could advance human knowledge and provide a route to truth.
Along with many French Enlightenment thinkers, Diderot treated the Catholic Church with grave suspicion. Although his own religious beliefs varied over his life from theism to atheism to deism, Diderot routinely attacked the conventional morality of the day and was even jailed for his writings. His "Pensees philisophiques" (philosophical thoughts) attacked both atheism and Christianity but was banned and ordered to be burned by the French government. Even the education-minded Encyclopedie, under Diderot's editorship, was occasionally prevented from production due to the heterodox and radical views in some of the minor articles.