The phrase "the best of all possible worlds" was coined by the German polymath and Enlightenment philosopher Gottfried Leibniz in his 1710 work Essais de Théodicée sur la bonté de Dieu, la liberté de l'homme et l'origine du mal, more commonly known simply as the Theodicy. The claim that the actual world is the best of all possible worlds is the central argument in Leibniz's theodicy, or his attempt to solve the problem of evil.

In the philosophy of religion, a theodicy is an argument that attempts to resolve the problem of evil that arises when all power and all goodness are simultaneously ascribed to God.