The following article is a contribution to the rich debate concerning happiness or fulfilment (eudaimonia) in Aristotle’s Nicomachean Ethics. It argues that eudaimonia is theōria in accordance with what Aristotle repeatedly says in Book X of the Nicomachean Ethics. However, happy life (eudaimōn bios) is a complex way of life which includes not only theoretical activity but also the exercising of other virtues including the so-called moral or social ones. The article shows that Aristotle differentiates between eudaimonia on the one (...) hand and the happy or fulfilled life (eudaimōn bios) on the other, and shows how this distinction clarifies Aristotle’s account of eudaimonia. (shrink)