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.

The problem of evil is the philosophical question of how to reconcile the existence of evil and suffering with an omnipotent, omnibenevolent, and omniscient God. There are currently differing definitions of these concepts. The best known presentation of the problem is attributed to the Greek philosopher Epicurus. It was popularized by David Hume.