Epicurus was born around 341 B.C., seven years after Plato's death, and grew up in the Athenian colony of Samos, an island in the Mediterranean Sea. He was about 19 when Aristotle died, and he studied philosophy under followers of Democritus and Plato. Epicurus founded his first philosophical schools in Mytilene and Lampsacus, before moving to Athens around 306 B.C. There Epicurus founded the Garden, a combination of philosophical community and school. The residents of the Garden put Epicurus' teachings into practice. Epicurus died from kidney stones around 271 or 270 B.C.

After Epicurus' death, Epicureanism continued to flourish as a philosophical movement. Communities of Epicureans sprang up throughout the Hellenistic world; along with, Stoicism it was one of the major philosophical schools competing for people's allegiances. Epicureanism went into decline with the rise of Christianity. Certain aspects of Epicurus' thought were revived during the Renaissance and early modern periods, when reaction against scholastic neo-Aristotelianism led thinkers to turn to mechanistic explanations of natural phenomena.

Epicurus is one of the major philosophers in the Hellenistic period, the three centuries following the death of Alexander the Great in 323 B.C. (and of Aristotle in 322 B.C.). Epicurus developed an unsparingly materialistic metaphysics, empiricist epistemology, and hedonistic ethics. Epicurus taught that the basic constituents of the world are atoms, uncut table bits of matter, flying through empty space, and he tried to explain all natural phenomena in atomic terms. Epicurus rejected the existence of Platonic forms and an immaterial soul, and he said that the gods have no influence on our lives. Epicurus also thought scepticism was untenable, and that we could gain knowledge of the world relying upon the senses. He taught that the point of all one's actions was to attain pleasure (conceived of as tranquillity) for oneself, and that this could be done by limiting one's desires and by banishing the fear of the gods and of death. Epicurus' gospel of freedom from fear proved to be quite popular, and communities of Epicureans flourished for centuries after his death.

Because of its denial of divine providence, Epicureanism was often charged in antiquity with being a godless philosophy, although Epicurus and his followers denied the charge. The main upshot of Epicurean theology is certainly negative, however. Epicurus' mechanistic explanations of natural phenomena are supposed to displace explanations that appeal to the will of the gods. In addition, Epicurus is one of the earliest philosophers we know of to have raised the Problem of Evil, arguing against the notion that the world is under the providential care of a loving deity by pointing out the manifold suffering in the world.

Despite this, Epicurus says that there are gods, but these gods are quite different from the popular conception of gods. We have a conception of the gods, says Epicurus, as supremely blessed and happy beings. Troubling oneself about the miseries of the world, or trying to administer the world, would be inconsistent with a life of tranquillity, says Epicurus, so the gods have no concern for us. In fact, they are unaware of our existence, and live eternally in the intermundia, the space between the cosmic. For Epicurus, the gods function mainly as ethical ideals, whose lives we can strive to emulate, but whose wrath we need not fear.

Ancient critics thought the Epicurean gods were a thin smoke-screen to hide Epicurus' atheism, and difficulties with a literal interpretation of Epicurus' sayings on the nature of the gods (for instance, it appears inconsistent with Epicurus' atomic theory to hold that any compound body, even a god, could be immortal) have led some scholars to conjecture that Epicurus' 'gods' are thought-constructs, and exist only in human minds as idealizations, i.e., the gods exist, but only as projections of what the most blessed life would be.