Stoicism, the philosophy of a school of Greek and Roman philosophers. They were called “Stoics” because the school's founder, Zeno of Cyprus (about 333 B.C.-261 B.C.), met his students at the Stoa Poikile (Painted Porch) on the north side of the market place in Athens. Through rational living and self-control, Zeno and his followers sought to find the source of virtue, and thus happiness, within themselves rather than in external things.

According to the Stoics, the world is a changing conflagration, or fire, which is limited and ordered by a creative force called Logos (world-reason), or God. Virtue consists of a man's consciously governing the “fires” of his action, or desires, by reason. The virtuous man is self-sufficient and undisturbed, not a slave of circumstances or emotions. Like Socrates, he faces events with calmness, living an honest and rational life. Stoics believed in the kinship and equality of all men, on the grounds that every person possesses a spark of the divine fire, or God. They saw the highest good in the contemplation of God and the universe.

Stoicism originated as a product of Greek and Oriental thought. Early Stoicism was influenced by Heraclitus (especially his theory that the world is a conflagration ordered by Logos) and by the contention of Socrates that an unexamined life is not worth living. Stoicism is similar to Cynicism and is opposed to Epicureanism.

The history of Stoicism is divided into three periods called the Old Stoa (300 B.C.-129 B.C.), the Middle Stoa (129 B.C.-30 B.C.), and the Late Stoa (30 B.C.-200 A.D.). Zeno, Cleanthes, and Chrysippus were important Stoic philosophers in the Old Stoa; Panaetius and Posidonius in the Middle Stoa; and Seneca, Epictetus, and Marcus Aurelius in the Late Stoa.

During the Late Stoa, the Stoic school shifted from Athens to Rome, where Stoicism stressed the importance of citizenship and honor. Roman Stoics often were advisers to Roman emperors, many of whom were themselves Stoics.

The influence of Stoicism is evident in Christian ideals such as simplicity, frugality, and equality. Stoic concepts of the universe influenced the pantheism of Spinoza and the doctrine of natural rights and natural law as found in the philosophy of Thomas Aquinas, Locke, Rousseau, and others.