The Difference Between the Democritean and Epicurean Philosophy of Nature () is a work completed in 1841 by German philosopher Karl Marx as his doctoral dissertation at the University of Jena. The thesis is a comparative study on atomism of Democritus and Epicurus on contingency and dedicated to Marx's friend, mentor, and future father-in-law, Ludwig von Westphalen. Francis Wheen describes it as "a daring and original piece of work in which Marx set out to show that theology must yield to the superior wisdom of philosophy".