His parents, Neocles and Chaerestrate, both Athenian-born, and his father a citizen, had emigrated to the Athenian settlement on the Aegean island of Samos about ten years before Epicurus's birth in February 341 BCE. As a boy he studied philosophy for four years under the Platonist teacher Pamphilus. At the age of 18 he went to Athens for his two-year term of military service. The playwright Menander served in the same age-class of the ephebes as Epicurus.

After the death of Alexander the Great, Perdiccas expelled the Athenian settlers on Samos to Colophon. After the completion of his military service, Epicurus joined his family there. He studied under Nausiphanes, who followed the teachings of Democritus. In 311/310 BCE Epicurus taught in Mytilene but caused strife and was forced to leave. He then founded a school in Lampsacus before returning to Athens in 306 BCE. There he founded The Garden, a school named for the garden he owned about halfway between the Stoa and the Academy that served as the school's meeting place.

Even though many of his teachings were heavily influenced by earlier thinkers, especially by Democritus, he differed in a significant way with Democritus on determinism. Epicurus would often deny this influence, denounce other philosophers as confused, and claim to be "self-taught".

Epicurus never married and had no known children. He suffered from kidney stones, to which he finally succumbed in 270 BCE at the age of 72, and despite the prolonged pain involved, he wrote to Idomeneus:

I have written this letter to you on a happy day to me, which is also the last day of my life. For I have been attacked by a painful inability to urinate, and also dysentery, so violent that nothing can be added to the violence of my sufferings. But the cheerfulness of my mind, which comes from the recollection of all my philosophical contemplation, counterbalances all these afflictions. And I beg you to take care of the children of Metrodorus, in a manner worthy of the devotion shown by the young man to me, and to philosophy.

Epicurus's school had a small but devoted following in his lifetime. The primary members were Hermarchus, the financier Idomeneus, Leonteus and his wife Themista, the satirist Colotes, the mathematician Polyaenus of Lampsacus, and Metrodorus of Lampsacus, the most famous popularizer of Epicureanism. His school was the first of the ancient Greek philosophical schools to admit women as a rule rather than an exception. The original school was based in Epicurus's home and garden. An inscription on the gate to the garden is recorded by Seneca in epistle XXI of Epistulae morales ad Lucilium:

Stranger, here you will do well to tarry; here our highest good is pleasure.

Epicurus emphasized friendship as an important ingredient of happiness, and the school resembled in many ways a community of friends living together. However, he also instituted a hierarchical system of levels among his followers, and had them swear an oath on his core tenets.

Prefiguring science and ethics

Epicurus is a key figure in the development of science and the scientific method because of his insistence that nothing should be believed, except that which was tested through direct observation and logical deduction. Many of his ideas about nature and physics presaged important scientific concepts of our time. He was a key figure in the Axial Age, the period from 800 BCE to 200 BCE, during which similarly revolutionary thinking appeared in China, India, Iran, the Near East, and Ancient Greece. His statement of the Ethic of Reciprocity as the foundation of ethics is the earliest in Ancient Greece, and he differs from the formulation of utilitarianism by John Stuart Mill by emphasizing the minimization of harm to oneself and others as the way to maximize happiness.

Epicurus's teachings represented a departure from the other major Greek thinkers of his period, and before, but was nevertheless founded on many of the same principles as Democritus. Like Democritus, he was an atomist, believing that the fundamental constituents of the world were indivisible little bits of matter (atoms, Greek atomos, indivisible) flying through empty space (khaos). Everything that occurs is the result of the atoms colliding, rebounding, and becoming entangled with one another, with no purpose or plan behind their motions. (Compare this with the modern study of particle physics.) His theory differs from the earlier atomism of Democritus because he admits that atoms do not always follow straight lines but their direction of motion may occasionally exhibit a 'swerve' (clinamen). This allowed him to avoid the determinism implicit in the earlier atomism and to affirm free will. (Compare this with the modern theory of quantum physics, which postulates a non-deterministic random motion of fundamental particles.)

He regularly admitted women and slaves into his school, introducing the new concept of fundamental human egalitarianism into Greek thought, and was one of the first Greeks to break from the god-fearing and god-worshiping tradition common at the time, even while affirming that religious activities are useful as a way to contemplate the gods and to use them as an example of the pleasant life. Epicurus participated in the activities of traditional Greek religion, but taught that one should avoid holding false opinions about the gods. The gods are immortal and blessed and men who ascribe any additional qualities that are alien to immortality and blessedness are, according to Epicurus, impious. The gods do not punish the bad and reward the good as the common man believes. The opinion of the crowd is, Epicurus claims, that the gods "send great evils to the wicked and great blessings to the righteous who model themselves after the gods," when in reality Epicurus believes the gods do not concern themselves at all with human beings.

It is not the man who denies the gods worshipped by the multitude, who is impious, but he who affirms of the gods what the multitude believes about them.

Pleasure as absence of suffering

Epicurus' philosophy is based on the theory that all good and bad derive from the sensations of pleasure and pain. What is good is what is pleasurable, and what is bad is what is painful. Pleasure and pain were ultimately, for Epicurus, the basis for the moral distinction between good and bad. If pain is chosen over pleasure in some cases it is only because it leads to a greater pleasure. Although Epicurus has been commonly misunderstood to advocate the rampant pursuit of pleasure, what he was really after was the absence of pain (both physical and mental, i.e., suffering) - a state of satiation and tranquility that was free of the fear of death and the retribution of the gods. When we do not suffer pain, we are no longer in need of pleasure, and we enter a state of 'perfect mental peace' (ataraxia).

Epicurus' teachings were introduced into medical philosophy and practice by the Epicurean doctor Asclepiades of Bithynia, who was the first physician who introduced Greek medicine in Rome. Asclepiades introduced the friendly, sympathetic, pleasing and painless treatment of patients. He advocated humane treatment of mental disorders, had insane persons freed from confinement and treated them with natural therapy, such as diet and massages. His teachings are surprisingly modern, therefore Asclepiades is considered to be a pioneer physician in psychotherapy, physical therapy and molecular medicine.

Epicurus explicitly warned against overindulgence because it often leads to pain. For instance, in what might be described as a "hangover" theory, Epicurus warned against pursuing love too ardently. However, having a circle of friends you can trust is one of the most important means for securing a tranquil life.

Epicurus also believed (contra Aristotle) that death was not to be feared. When a man dies, he does not feel the pain of death because he no longer is and he therefore feels nothing. Therefore, as Epicurus famously said, "death is nothing to us." When we exist death is not, and when death exists we are not. All sensation and consciousness ends with death and therefore in death there is neither pleasure nor pain. The fear of death arises from the false belief that in death there is awareness.

In this context Epicurus said: Non fui, fui, non sum, non curo (I was not; I have been; I am not; I do not care) — which is inscribed on the gravestones of his followers and seen on many ancient gravestones of the Roman Empire. This quote is often used today at humanist funerals.

The "Epicurean paradox" is a version of the problem of evil. It is a trilemma argument (God is omnipotent, God is good, but Evil exists); or more commonly seen as this quote:

“Is God willing to prevent evil, but not able?Then he is not omnipotent.Is he able, but not willing?Then he is malevolent.Is he both able and willing?Then whence cometh evil?Is he neither able nor willing?Then why call him God?”

This argument was a type favoured by the ancient Greek skeptics, and may have been wrongly attributed to Epicurus by Lactantius, who, from his Christian perspective, regarded Epicurus as an atheist. According to Reinhold F. Glei, it is settled that the argument of theodicy is from an academic source which is not only not epicurean, but even anti-epicurean. The earliest extant version of this trilemma appears in the writings of the skeptic Sextus Empiricus.

Epicurus didn’t deny the existence of gods. Instead, he stated that what gods there may be do not concern themselves with us, and thus would not seek to punish us either in this or any other life.

Epicurus emphasized the senses in his epistemology, and his Principle of Multiple Explanations ("if several theories are consistent with the observed data, retain them all") is an early contribution to the philosophy of science.

There are also some things for which it is not enough to state a single cause, but several, of which one, however, is the case. Just as if you were to see the lifeless corpse of a man lying far away, it would be fitting to list all the causes of death in order to make sure that the single cause of this death may be stated. For you would not be able to establish conclusively that he died by the sword or of cold or of illness or perhaps by poison, but we know that there is something of this kind that happened to him.

In contrast to the Stoics, Epicureans showed little interest in participating in the politics of the day, since doing so leads to trouble. He instead advocated seclusion. His garden can be compared to present-day commune. This principle is epitomized by the phrase lathe bi?sas ???? ?????? (Plutarchus De latenter vivendo 1128c; Flavius Philostratus Vita Apollonii 8.28.12), meaning "live secretly", "get through life without drawing attention to yourself", i. e. live without pursuing glory or wealth or power, but anonymously, enjoying little things like food, the company of friends, etc.

As an ethical guideline, Epicurus emphasized minimizing harm and maximizing happiness of oneself and others:

It is impossible to live a pleasant life without living wisely and well and justly (agreeing "neither to harm nor be harmed"), and it is impossible to live wisely and well and justly without living a pleasant life.

Elements of Epicurean philosophy have resonated and resurfaced in various diverse thinkers and movements throughout Western intellectual history.

The atomic poems (such as 'All Things are Governed by Atoms') and natural philosophy of Margaret Cavendish were influenced by Epicurus.

His emphasis minimizing harm and maximizing happiness in his formulation of the Ethic of Reciprocity was later picked up by the democratic thinkers of the French Revolution, and others, like John Locke, who wrote that people had a right to "life, liberty, and property." To Locke, one's own body was part of their property, and thus one's right to property would theoretically guarantee safety for their persons, as well as their possessions.

This triad, as well as the egalitarianism of Epicurus, was carried forward into the American freedom movement and Declaration of Independence, by the American founding father, Thomas Jefferson, as "all men are created equal" and endowed with certain "inalienable rights such as life, liberty, and the pursuit of happiness." Jefferson considered himself an Epicurean. [1]

In An Enquiry Concerning Human Understanding, David Hume uses Epicurus as a character for explaining the impossibility of our knowing God to be any greater or better than his creation proves him to be.

Karl Marx's doctoral thesis was on "The Difference Between the Democritean and Epicurean Philosophy of Nature." [2]

Epicurus was first to assert human freedom as coming from a fundamental indeterminism in the motion of atoms. This has led some philosophers to think that for Epicurus free will was caused directly by chance. In his "On the Nature of Things," Lucretius appears to suggest this in the best-known passage on Epicurus's position. But in his Letter to Menoeceus, Epicurus follows Aristotle and clearly identifies three possible causes - "some things happen of necessity, others by chance, others through our own agency." Aristotle said some things "depend on us" (eph hemin). Epicurus agreed, and said it is to these last things that praise and blame naturally attach. For Epicurus, the chance "swerve" of the atoms simply defeated determinism to leave room for autonomous agency.

Epicurus was also a significant source of inspiration and interest for both Arthur Schopenhauer, having particular influence on the famous pessimist's views on suffering and death, as well as one of Schopenhauer's successors: Friedrich Nietzsche. Nietzsche cites his affinities to Epicurus in a number of his works, including The Gay Science, Beyond Good and Evil, and his private letters to Peter Gast. Nietzsche was attracted to, among other things, Epicurus's ability to maintain a cheerful philosophical outlook in the face of painful physical ailments. Nietzsche also suffered from a number of sicknesses during his lifetime. However, he thought that Epicurus's conception of happiness as freedom from anxiety was too passive and negative.

The only surviving complete works by Epicurus are three letters, which are to be found in book X of Diogenes Laertius's Lives of Eminent Philosophers, and two groups of quotes: the Principal Doctrines, reported as well in Diogenes's book X, and the Vatican Sayings, preserved in a manuscript from the Vatican Library.

Numerous fragments of his thirty-seven volume treatise On Nature have been found among the charred papyrus fragments at the Villa of the Papyri at Herculaneum. In addition, other Epicurean writings found at Herculaneum contain important quotations from his other works. Moreover, numerous fragments and testimonies are found throughout ancient Greek and Roman literature, a collection of which can be found in Usener's Epicurea.

According to Diskin Clay, Epicurus himself established a custom of celebrating his birthday annually with common meals, befitting his stature as hero ctistes (or founding hero) of the Garden. He ordained in his will annual memorial feasts for himself on the same date (10th of Gamelion month). Epicurean communities continued this tradition, referring to Epicurus as their "savior" (soter) and celebrating him as hero. Lucretius apotheosized Epicurus as the main character of his epic poem De rerum natura. The hero cult of Epicurus may have operated as a Garden variety civic religion. However, clear evidence of an Epicurean hero cult, as well as the cult itself, seems buried by the weight of posthumous philosophical interpretation. Epicurus' cheerful demeanor, as he continued to work despite dying from a painful stone blockage of his urinary tract lasting a fortnight, according to his successor Hermarchus and reported by his biographer Diogenes Laertius, further enhanced his status among his followers.

In Canto X Circle 6 ("Where the heretics lie") of Dante's Inferno, Epicurus and his followers are criticized for supporting a materialistic ideal.

Epicurus the Sage was a 2 part comic book by William Messner-Loebs and Sam Kieth, portraying Epicurus as "the only sane philosopher." by anachronistically bringing together Epicurus with many other well known Greek philosophers, republished as graphic novel by the Wildstorm branch of DC Comics.