Eudaimonia (Greek: εὐδαιμονία) is a central concept in Aristotle's Nicomachean Ethics, a work that has significantly influenced much philosophical thinking about ethics, morality, and the nature of the good life. 

The Greek term is still widely used by philosophers in modern languages, including English. It means something on the order of "well-being" or "human flourishing." Aristotle himself contrasts it with "hēdonḗ" (Greek:  ἡδονή) or immediate (especially sensual) pleasure. Living the good or eudaimonic life is our ultimate goal, of course; no one would say that they want to live badly or not flourish in some way. The philosophical quandary comes in attempting to define what actually constitutes a good life.

Aristotle himself suggests that it is one of “virtuous activity in accordance with reason.” He sees the ultimate form of eudaimonia as the philosophical life because, as reason is the highest and most distinctively human capability, the best human life is the one most in accord with and most focused on exercising reason. Stoics tended to favor a life undisturbed by the passions (apatheia) in which one attempted to understand and act in harmony with the natural laws of the universe. The Epicureans emphasized a goal of ataraxia (tranquility) and a life somewhat withdrawn from the world, achieving eudaimonia by "cultivating one's garden."